diff --git a/audio_getter.py b/audio_getter.py
index a771964..ee75199 100644
--- a/audio_getter.py
+++ b/audio_getter.py
@@ -6,6 +6,7 @@
 
 import ffmpeg
 import numpy as np
+import sounddevice as sd
 
 from common import SAMPLE_RATE
 
@@ -90,7 +91,6 @@ def work(self, output_queue: queue.SimpleQueue[np.array]):
 class DeviceAudioGetter():
 
     def __init__(self, device_index: int, frame_duration: float) -> None:
-        import sounddevice as sd
         if device_index:
             sd.default.device[0] = device_index
         sd.default.dtype[0] = np.float32
diff --git a/audio_slicer.py b/audio_slicer.py
index 5a24c5b..bd372ac 100644
--- a/audio_slicer.py
+++ b/audio_slicer.py
@@ -21,7 +21,7 @@ class VAD:
     def __init__(self):
         self.model = _init_jit_model("silero_vad.jit")
 
-    def is_speech(self, audio, threshold: float = 0.5, sampling_rate: int = 16000):
+    def is_speech(self, audio: np.array, threshold: float = 0.5, sampling_rate: int = 16000):
         if not torch.is_tensor(audio):
             try:
                 audio = torch.Tensor(audio)
@@ -55,7 +55,7 @@ def __init__(self, frame_duration: float, continuous_no_speech_threshold: float,
         self.counter = 0
         self.last_slice_second = 0.0
 
-    def put(self, audio):
+    def put(self, audio: np.array):
         self.counter += 1
         if self.vad.is_speech(audio, self.vad_threshold, self.sampling_rate):
             self.audio_buffer.append(audio)
diff --git a/audio_transcriber.py b/audio_transcriber.py
index 13cceaa..3c31307 100644
--- a/audio_transcriber.py
+++ b/audio_transcriber.py
@@ -3,6 +3,8 @@
 from scipy.io.wavfile import write as write_audio
 
 import numpy as np
+import whisper
+from faster_whisper import WhisperModel
 from openai import OpenAI
 
 import filters
@@ -11,7 +13,7 @@
 TEMP_AUDIO_FILE_NAME = 'temp.wav'
 
 
-def _filter_text(text, whisper_filters):
+def _filter_text(text: str, whisper_filters: str):
     filter_name_list = whisper_filters.split(',')
     for filter_name in filter_name_list:
         filter = getattr(filters, filter_name)
@@ -23,9 +25,8 @@ def _filter_text(text, whisper_filters):
 
 class OpenaiWhisper():
 
-    def __init__(self, model) -> None:
+    def __init__(self, model: str) -> None:
         print("Loading whisper model: {}".format(model))
-        import whisper
         self.model = whisper.load_model(model)
 
     def transcribe(self, audio: np.array, **transcribe_options) -> str:
@@ -48,9 +49,8 @@ def work(self, input_queue: queue.SimpleQueue[TranslationTask],
 
 class FasterWhisper(OpenaiWhisper):
 
-    def __init__(self, model) -> None:
+    def __init__(self, model: str) -> None:
         print("Loading faster-whisper model: {}".format(model))
-        from faster_whisper import WhisperModel
         self.model = WhisperModel(model)
 
     def transcribe(self, audio: np.array, **transcribe_options) -> str:
diff --git a/filters.py b/filters.py
index 1ae4626..78ffceb 100644
--- a/filters.py
+++ b/filters.py
@@ -1,13 +1,13 @@
 import re
 
 
-def emoji_filter(text):
+def emoji_filter(text: str):
     return re.sub(
         r'[\U0001F600-\U0001F64F\U0001F300-\U0001F5FF\U0001F680-\U0001F6FF\U0001F1E0-\U0001F1FF]+',
         '', text)
 
 
-def japanese_stream_filter(text):
+def japanese_stream_filter(text: str):
     for filter_pattern in [
             r'【.+】', r'ご視聴ありがとうございました', r'チャンネル登録をお願いいたします', r'ご視聴いただきありがとうございます', r'チャンネル登録してね',
             r'字幕視聴ありがとうございました', r'動画をご覧頂きましてありがとうございました', r'次の動画でお会いしましょう', r'最後までご視聴頂きありがとうございました',
diff --git a/gpt_translator.py b/gpt_translator.py
index 6f6bab7..acfa820 100644
--- a/gpt_translator.py
+++ b/gpt_translator.py
@@ -9,7 +9,7 @@
 from common import TranslationTask
 
 
-def _translate_by_gpt(client, translation_task, assistant_prompt, model, history_messages=[]):
+def _translate_by_gpt(client: OpenAI, translation_task: TranslationTask, assistant_prompt: str, model: str, history_messages: list=[]):
     # https://platform.openai.com/docs/api-reference/chat/create?lang=python
     try:
         system_prompt = "You are a translation engine."
@@ -33,14 +33,14 @@ def _translate_by_gpt(client, translation_task, assistant_prompt, model, history
 
 class ParallelTranslator():
 
-    def __init__(self, prompt, model, timeout):
+    def __init__(self, prompt: str, model: str, timeout: int):
         self.prompt = prompt
         self.model = model
         self.timeout = timeout
         self.client = OpenAI()
         self.processing_queue = deque()
 
-    def trigger(self, translation_task):
+    def trigger(self, translation_task: TranslationTask):
         self.processing_queue.append(translation_task)
         translation_task.start_time = datetime.utcnow()
         thread = threading.Thread(target=_translate_by_gpt,
@@ -73,7 +73,7 @@ def work(self, input_queue: queue.SimpleQueue[TranslationTask],
 
 class SerialTranslator():
 
-    def __init__(self, prompt, model, timeout, history_size):
+    def __init__(self, prompt: str, model: str, timeout: int, history_size: int):
         self.prompt = prompt
         self.model = model
         self.timeout = timeout
diff --git a/result_exporter.py b/result_exporter.py
index 654566e..3f381e2 100644
--- a/result_exporter.py
+++ b/result_exporter.py
@@ -11,7 +11,7 @@ def _send_to_cqhttp(url: str, token: str, text: str):
     requests.post(url, headers=headers, data=data)
 
 
-def _sec2str(second):
+def _sec2str(second: float):
     dt = datetime.utcfromtimestamp(second)
     result = dt.strftime('%H:%M:%S')
     result += ',' + str(round(second * 10 % 10))