diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 9e863a246..3b6b6d047 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -18,7 +18,7 @@ jobs:
       matrix:
         include:
         - os: [macos-11]
-          python: '3.7'
+          python: '3.8'
           python_architecture: 'x64'
           pip_cache_path: ~/Library/Caches/pip
           voicevox_resource_version: '0.9.2'
@@ -408,7 +408,7 @@ jobs:
         include:
         # Windows CPU
         - os: windows-2019
-          python: '3.7'
+          python: '3.8'
           python_architecture: 'x64'
           voicevox_resource_version: '0.9.2'
           voicevox_core_version: '0.9.0'
@@ -421,7 +421,7 @@ jobs:
           pip_cache_path: ~\AppData\Local\pip\Cache
         # Windows NVIDIA GPU
         - os: windows-2019
-          python: '3.7'
+          python: '3.8'
           python_architecture: 'x64'
           voicevox_resource_version: '0.9.2'
           voicevox_core_version: '0.9.0'
diff --git a/Dockerfile b/Dockerfile
index 336697162..367fdf604 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -145,7 +145,7 @@ RUN <<EOF
     rm -rf /var/lib/apt/lists/*
 EOF
 
-ARG PYTHON_VERSION=3.7.12
+ARG PYTHON_VERSION=3.8.10
 # FIXME: Lock pyenv version with git tag
 # 90d0d20508a91e7ea1e609e8aa9f9d1a28bb563e (including 3.7.12) not released yet (2021-09-12)
 ARG PYENV_VERSION=master
diff --git a/run.py b/run.py
index b04afc11d..56a95e294 100644
--- a/run.py
+++ b/run.py
@@ -10,6 +10,7 @@
 from typing import List, Optional
 
 import numpy as np
+import pyworld as pw
 import soundfile
 import uvicorn
 from fastapi import FastAPI, HTTPException, Request, Response
@@ -128,8 +129,6 @@ def create_accent_phrases(text: str, speaker_id: int) -> List[AccentPhrase]:
     def synthesis_world_params(
         query: AudioQuery, base_speaker: int, target_speaker: int
     ):
-        import pyworld as pw
-
         base_wave = engine.synthesis(query=query, speaker_id=base_speaker).astype(
             "float"
         )
@@ -405,8 +404,6 @@ def synthesis_morphing(
         モーフィングの割合は`morph_rate`で指定でき、0.0でベースの話者、1.0でターゲットの話者に近づきます。
         """
 
-        import pyworld as pw
-
         if morph_rate < 0.0 or morph_rate > 1.0:
             raise HTTPException(
                 status_code=422, detail="morph_rateは0.0から1.0の範囲で指定してください"