diff --git a/common/log.py b/common/log.py
index 679bb2c..71b5e63 100644
--- a/common/log.py
+++ b/common/log.py
@@ -14,4 +14,5 @@ log_format = (
     "<g>{time:MM-DD HH:mm:ss}</g> |<lvl>{level:^8}</lvl>| {file}:{line} | {message}"
 )
 
+# logger.add(SAFE_STDOUT, format=log_format, backtrace=True, diagnose=True, level="TRACE")
 logger.add(SAFE_STDOUT, format=log_format, backtrace=True, diagnose=True)
diff --git a/common/tts_model.py b/common/tts_model.py
index e09787e..9e2171d 100644
--- a/common/tts_model.py
+++ b/common/tts_model.py
@@ -222,12 +222,14 @@ class ModelHolder:
         self.current_model: Optional[Model] = None
         self.model_names: list[str] = []
         self.models: list[Model] = []
+        self.models_info: list[dict[str, Union[str, list[str]]]] = []
         self.refresh()
 
     def refresh(self):
         self.model_files_dict = {}
         self.model_names = []
         self.current_model = None
+        self.models_info = []
 
         model_dirs = [d for d in self.root_dir.iterdir() if d.is_dir()]
         for model_dir in model_dirs:
@@ -247,26 +249,19 @@ class ModelHolder:
                 continue
             self.model_files_dict[model_dir.name] = model_files
             self.model_names.append(model_dir.name)
-
-    def models_info(self):
-        if hasattr(self, "_models_info"):
-            return self._models_info
-        result = []
-        for name, files in self.model_files_dict.items():
-            # Get styles
-            config_path = self.root_dir / name / "config.json"
             hps = utils.get_hparams_from_file(config_path)
             style2id: dict[str, int] = hps.data.style2id
             styles = list(style2id.keys())
-            result.append(
+            spk2id: dict[str, int] = hps.data.spk2id
+            speakers = list(spk2id.keys())
+            self.models_info.append(
                 {
-                    "name": name,
-                    "files": [str(f) for f in files],
+                    "name": model_dir.name,
+                    "files": [str(f) for f in model_files],
                     "styles": styles,
+                    "speakers": speakers,
                 }
             )
-        self._models_info = result
-        return result
 
     def load_model(self, model_name: str, model_path_str: str):
         model_path = Path(model_path_str)
diff --git a/server_editor.py b/server_editor.py
index afb9321..402116f 100644
--- a/server_editor.py
+++ b/server_editor.py
@@ -16,13 +16,13 @@ import zipfile
 from datetime import datetime
 from io import BytesIO
 from pathlib import Path
-import yaml
+from typing import Optional
 
 import numpy as np
-import pyopenjtalk
 import requests
 import torch
 import uvicorn
+import yaml
 from fastapi import APIRouter, FastAPI, HTTPException, status
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse, Response
@@ -43,8 +43,7 @@ from common.constants import (
 from common.log import logger
 from common.tts_model import ModelHolder
 from text.japanese import g2kata_tone, kata_tone2phone_tone, text_normalize
-from text.user_dict import apply_word, update_dict, read_dict, rewrite_word, delete_word
-
+from text.user_dict import apply_word, delete_word, read_dict, rewrite_word, update_dict
 
 # ---フロントエンド部分に関する処理---
 
@@ -230,7 +229,7 @@ async def normalize_text(item: TextRequest):
 
 @router.get("/models_info")
 def models_info():
-    return model_holder.models_info()
+    return model_holder.models_info
 
 
 class SynthesisRequest(BaseModel):
@@ -250,6 +249,7 @@ class SynthesisRequest(BaseModel):
     silenceAfter: float = 0.5
     pitchScale: float = 1.0
     intonationScale: float = 1.0
+    speaker: Optional[str] = None
 
 
 @router.post("/synthesis", response_class=AudioResponse)
@@ -275,6 +275,13 @@ def synthesis(request: SynthesisRequest):
     ]
     phone_tone = kata_tone2phone_tone(kata_tone_list)
     tone = [t for _, t in phone_tone]
+    try:
+        sid = 0 if request.speaker is None else model.spk2id[request.speaker]
+    except KeyError:
+        raise HTTPException(
+            status_code=400,
+            detail=f"Speaker {request.speaker} not found in {model.spk2id}",
+        )
     sr, audio = model.infer(
         text=text,
         language=request.language.value,
@@ -291,6 +298,7 @@ def synthesis(request: SynthesisRequest):
         line_split=False,
         pitch_scale=request.pitchScale,
         intonation_scale=request.intonationScale,
+        sid=sid,
     )
 
     with BytesIO() as wavContent:
diff --git a/text/japanese.py b/text/japanese.py
index b18bc68..fea0eaa 100644
--- a/text/japanese.py
+++ b/text/japanese.py
@@ -4,7 +4,9 @@ import re
 import unicodedata
 from pathlib import Path
 
-import pyopenjtalk
+from . import pyopenjtalk_worker as pyopenjtalk
+
+pyopenjtalk.initialize()
 from num2words import num2words
 from transformers import AutoTokenizer
 
diff --git a/text/pyopenjtalk_worker/__init__.py b/text/pyopenjtalk_worker/__init__.py
new file mode 100644
index 0000000..7aa0d0e
--- /dev/null
+++ b/text/pyopenjtalk_worker/__init__.py
@@ -0,0 +1,126 @@
+"""
+Run the pyopenjtalk worker in a separate process
+to avoid user dictionary access error
+"""
+
+from typing import Optional, Any
+
+from .worker_common import WORKER_PORT
+from .worker_client import WorkerClient
+
+from common.log import logger
+
+WORKER_CLIENT: Optional[WorkerClient] = None
+
+# pyopenjtalk interface
+
+# g2p: not used
+
+
+def run_frontend(text: str) -> list[dict[str, Any]]:
+    assert WORKER_CLIENT
+    ret = WORKER_CLIENT.dispatch_pyopenjtalk("run_frontend", text)
+    assert isinstance(ret, list)
+    return ret
+
+
+def make_label(njd_features) -> list[str]:
+    assert WORKER_CLIENT
+    ret = WORKER_CLIENT.dispatch_pyopenjtalk("make_label", njd_features)
+    assert isinstance(ret, list)
+    return ret
+
+
+def mecab_dict_index(path: str, out_path: str, dn_mecab: Optional[str] = None):
+    assert WORKER_CLIENT
+    WORKER_CLIENT.dispatch_pyopenjtalk("mecab_dict_index", path, out_path, dn_mecab)
+
+
+def update_global_jtalk_with_user_dict(path: str):
+    assert WORKER_CLIENT
+    WORKER_CLIENT.dispatch_pyopenjtalk("update_global_jtalk_with_user_dict", path)
+
+
+def unset_user_dict():
+    assert WORKER_CLIENT
+    WORKER_CLIENT.dispatch_pyopenjtalk("unset_user_dict")
+
+
+# initialize module when imported
+
+
+def initialize(port: int = WORKER_PORT):
+    import time
+    import socket
+    import sys
+    import atexit
+    import signal
+
+    logger.debug("initialize")
+    global WORKER_CLIENT
+    if WORKER_CLIENT:
+        return
+
+    client = None
+    try:
+        client = WorkerClient(port)
+    except (socket.timeout, socket.error):
+        logger.debug("try starting pyopenjtalk worker server")
+        import os
+        import subprocess
+
+        worker_pkg_path = os.path.relpath(
+            os.path.dirname(__file__), os.getcwd()
+        ).replace(os.sep, ".")
+        args = [sys.executable, "-m", worker_pkg_path, "--port", str(port)]
+        # new session, new process group
+        if sys.platform.startswith("win"):
+            cf = subprocess.CREATE_NEW_CONSOLE | subprocess.CREATE_NEW_PROCESS_GROUP  # type: ignore
+            si = subprocess.STARTUPINFO()  # type: ignore
+            si.dwFlags |= subprocess.STARTF_USESHOWWINDOW  # type: ignore
+            si.wShowWindow = subprocess.SW_HIDE  # type: ignore
+            subprocess.Popen(args, creationflags=cf, startupinfo=si)
+        else:
+            # align with Windows behavior
+            # start_new_session is same as specifying setsid in preexec_fn
+            subprocess.Popen(args, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, start_new_session=True)  # type: ignore
+
+        # wait until server listening
+        count = 0
+        while True:
+            try:
+                client = WorkerClient(port)
+                break
+            except socket.error:
+                time.sleep(1)
+                count += 1
+                # 10: max number of retries
+                if count == 10:
+                    raise TimeoutError("サーバーに接続できませんでした")
+
+    WORKER_CLIENT = client
+    atexit.register(terminate)
+
+    # when the process is killed
+    def signal_handler(signum, frame):
+        terminate()
+
+    signal.signal(signal.SIGTERM, signal_handler)
+
+
+# top-level declaration
+def terminate():
+    logger.debug("terminate")
+    global WORKER_CLIENT
+    if not WORKER_CLIENT:
+        return
+
+    # repare for unexpected errors
+    try:
+        if WORKER_CLIENT.status() == 1:
+            WORKER_CLIENT.quit_server()
+    except Exception as e:
+        logger.error(e)
+
+    WORKER_CLIENT.close()
+    WORKER_CLIENT = None
diff --git a/text/pyopenjtalk_worker/__main__.py b/text/pyopenjtalk_worker/__main__.py
new file mode 100644
index 0000000..3bb6b53
--- /dev/null
+++ b/text/pyopenjtalk_worker/__main__.py
@@ -0,0 +1,16 @@
+import argparse
+
+from .worker_server import WorkerServer
+from .worker_common import WORKER_PORT
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--port", type=int, default=WORKER_PORT)
+    args = parser.parse_args()
+    server = WorkerServer()
+    server.start_server(port=args.port)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/text/pyopenjtalk_worker/worker_client.py b/text/pyopenjtalk_worker/worker_client.py
new file mode 100644
index 0000000..86d8969
--- /dev/null
+++ b/text/pyopenjtalk_worker/worker_client.py
@@ -0,0 +1,55 @@
+from typing import Any
+import socket
+
+from .worker_common import RequestType, receive_data, send_data
+
+from common.log import logger
+
+
+class WorkerClient:
+    def __init__(self, port: int) -> None:
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        # 5: timeout
+        sock.settimeout(5)
+        sock.connect((socket.gethostname(), port))
+        self.sock = sock
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.close()
+
+    def close(self):
+        self.sock.close()
+
+    def dispatch_pyopenjtalk(self, func: str, *args, **kwargs):
+        data = {
+            "request-type": RequestType.PYOPENJTALK,
+            "func": func,
+            "args": args,
+            "kwargs": kwargs,
+        }
+        logger.trace(f"client sends request: {data}")
+        send_data(self.sock, data)
+        logger.trace("client sent request successfully")
+        response = receive_data(self.sock)
+        logger.trace(f"client received response: {response}")
+        return response.get("return")
+
+    def status(self):
+        data = {"request-type": RequestType.STATUS}
+        logger.trace(f"client sends request: {data}")
+        send_data(self.sock, data)
+        logger.trace("client sent request successfully")
+        response = receive_data(self.sock)
+        logger.trace(f"client received response: {response}")
+        return response.get("client-count")
+
+    def quit_server(self):
+        data = {"request-type": RequestType.QUIT_SERVER}
+        logger.trace(f"client sends request: {data}")
+        send_data(self.sock, data)
+        logger.trace("client sent request successfully")
+        response = receive_data(self.sock)
+        logger.trace(f"client received response: {response}")
diff --git a/text/pyopenjtalk_worker/worker_common.py b/text/pyopenjtalk_worker/worker_common.py
new file mode 100644
index 0000000..606d0c3
--- /dev/null
+++ b/text/pyopenjtalk_worker/worker_common.py
@@ -0,0 +1,44 @@
+from typing import Any, Optional, Final
+from enum import IntEnum, auto
+import socket
+import json
+
+WORKER_PORT: Final[int] = 7861
+HEADER_SIZE: Final[int] = 4
+
+
+class RequestType(IntEnum):
+    STATUS = auto()
+    QUIT_SERVER = auto()
+    PYOPENJTALK = auto()
+
+
+class ConnectionClosedException(Exception):
+    pass
+
+
+# socket communication
+
+
+def send_data(sock: socket.socket, data: dict[str, Any]):
+    json_data = json.dumps(data).encode()
+    header = len(json_data).to_bytes(HEADER_SIZE, byteorder="big")
+    sock.sendall(header + json_data)
+
+
+def _receive_until(sock: socket.socket, size: int):
+    data = b""
+    while len(data) < size:
+        part = sock.recv(size - len(data))
+        if part == b"":
+            raise ConnectionClosedException("接続が閉じられました")
+        data += part
+
+    return data
+
+
+def receive_data(sock: socket.socket) -> dict[str, Any]:
+    header = _receive_until(sock, HEADER_SIZE)
+    data_length = int.from_bytes(header, byteorder="big")
+    body = _receive_until(sock, data_length)
+    return json.loads(body.decode())
diff --git a/text/pyopenjtalk_worker/worker_server.py b/text/pyopenjtalk_worker/worker_server.py
new file mode 100644
index 0000000..6babd91
--- /dev/null
+++ b/text/pyopenjtalk_worker/worker_server.py
@@ -0,0 +1,118 @@
+import pyopenjtalk
+import socket
+import select
+import time
+
+from .worker_common import (
+    ConnectionClosedException,
+    RequestType,
+    receive_data,
+    send_data,
+)
+
+from common.log import logger
+
+# To make it as fast as possible
+# Probably faster than calling getattr every time
+_PYOPENJTALK_FUNC_DICT = {
+    "run_frontend": pyopenjtalk.run_frontend,
+    "make_label": pyopenjtalk.make_label,
+    "mecab_dict_index": pyopenjtalk.mecab_dict_index,
+    "update_global_jtalk_with_user_dict": pyopenjtalk.update_global_jtalk_with_user_dict,
+    "unset_user_dict": pyopenjtalk.unset_user_dict,
+}
+
+
+class WorkerServer:
+    def __init__(self) -> None:
+        self.client_count: int = 0
+        self.quit: bool = False
+
+    def handle_request(self, request):
+        request_type = None
+        try:
+            request_type = RequestType(request.get("request-type"))
+        except Exception:
+            return {
+                "success": False,
+                "reason": "request-type is invalid",
+            }
+
+        if request_type:
+            if request_type == RequestType.STATUS:
+                response = {
+                    "success": True,
+                    "client-count": self.client_count,
+                }
+            elif request_type == RequestType.QUIT_SERVER:
+                self.quit = True
+                response = {"success": True}
+            elif request_type == RequestType.PYOPENJTALK:
+                func_name = request.get("func")
+                assert isinstance(func_name, str)
+                func = _PYOPENJTALK_FUNC_DICT[func_name]
+                args = request.get("args")
+                kwargs = request.get("kwargs")
+                assert isinstance(args, list)
+                assert isinstance(kwargs, dict)
+                ret = func(*args, **kwargs)
+                response = {"success": True, "return": ret}
+            else:
+                # NOT REACHED
+                response = request
+
+        return response
+
+    def start_server(self, port: int, no_client_timeout: int = 30):
+        logger.info("start pyopenjtalk worker server")
+        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as server_socket:
+            server_socket.bind((socket.gethostname(), port))
+            server_socket.listen()
+            sockets = [server_socket]
+            no_client_since = time.time()
+            while True:
+                if self.client_count == 0:
+                    if no_client_since is None:
+                        no_client_since = time.time()
+                    elif (time.time() - no_client_since) > no_client_timeout:
+                        logger.info("quit because there is no client")
+                        return
+                else:
+                    no_client_since = None
+
+                ready_sockets, _, _ = select.select(sockets, [], [], 0.1)
+                for sock in ready_sockets:
+                    if sock is server_socket:
+                        logger.info("new client connected")
+                        client_socket, _ = server_socket.accept()
+                        sockets.append(client_socket)
+                        self.client_count += 1
+                    else:
+                        # client
+                        try:
+                            request = receive_data(sock)
+                        except Exception as e:
+                            sock.close()
+                            sockets.remove(sock)
+                            self.client_count -= 1
+                            # unexpected disconnections
+                            if not isinstance(e, ConnectionClosedException):
+                                logger.error(e)
+
+                            logger.info("close connection")
+                            continue
+
+                        logger.trace(f"server received request: {request}")
+
+                        response = self.handle_request(request)
+                        logger.trace(f"server sends response: {response}")
+                        try:
+                            send_data(sock, response)
+                            logger.trace("server sent response successfully")
+                        except Exception:
+                            logger.warning(
+                                "an exception occurred during sending responce"
+                            )
+                        if self.quit:
+                            logger.info("quit pyopenjtalk worker server")
+                            return
diff --git a/text/user_dict/__init__.py b/text/user_dict/__init__.py
index c12b3d1..95515cb 100644
--- a/text/user_dict/__init__.py
+++ b/text/user_dict/__init__.py
@@ -12,7 +12,9 @@ from typing import Dict, List, Optional
 from uuid import UUID, uuid4
 
 import numpy as np
-import pyopenjtalk
+from .. import pyopenjtalk_worker as pyopenjtalk
+
+pyopenjtalk.initialize()
 from fastapi import HTTPException
 
 from .word_model import UserDictWord, WordTypes