diff --git a/voicevox_engine/kana_parser.py b/voicevox_engine/kana_parser.py
index 711b6a7de..8e0ff845a 100644
--- a/voicevox_engine/kana_parser.py
+++ b/voicevox_engine/kana_parser.py
@@ -3,16 +3,16 @@
 from .model import AccentPhrase, Mora, ParseKanaError, ParseKanaErrorCode
 from .mora_list import openjtalk_text2mora
 
-LOOP_LIMIT = 300
-UNVOICE_SYMBOL = "_"
-ACCENT_SYMBOL = "'"
-NOPAUSE_DELIMITER = "/"
-PAUSE_DELIMITER = "、"
-WIDE_INTERROGATION_MARK = "？"
-
-text2mora_with_unvoice = {}
+_LOOP_LIMIT = 300
+_UNVOICE_SYMBOL = "_"
+_ACCENT_SYMBOL = "'"
+_NOPAUSE_DELIMITER = "/"
+_PAUSE_DELIMITER = "、"
+_WIDE_INTERROGATION_MARK = "？"
+
+_text2mora_with_unvoice = {}
 for text, (consonant, vowel) in openjtalk_text2mora.items():
-    text2mora_with_unvoice[text] = Mora(
+    _text2mora_with_unvoice[text] = Mora(
         text=text,
         consonant=consonant if len(consonant) > 0 else None,
         consonant_length=0 if len(consonant) > 0 else None,
@@ -22,7 +22,7 @@
         is_interrogative=False,
     )
     if vowel in ["a", "i", "u", "e", "o"]:
-        text2mora_with_unvoice[UNVOICE_SYMBOL + text] = Mora(
+        _text2mora_with_unvoice[_UNVOICE_SYMBOL + text] = Mora(
             text=text,
             consonant=consonant if len(consonant) > 0 else None,
             consonant_length=0 if len(consonant) > 0 else None,
@@ -48,7 +48,7 @@ def _text_to_accent_phrase(phrase: str) -> AccentPhrase:
     outer_loop = 0
     while base_index < len(phrase):
         outer_loop += 1
-        if phrase[base_index] == ACCENT_SYMBOL:
+        if phrase[base_index] == _ACCENT_SYMBOL:
             if len(moras) == 0:
                 raise ParseKanaError(ParseKanaErrorCode.ACCENT_TOP, text=phrase)
             if accent_index is not None:
@@ -57,21 +57,21 @@ def _text_to_accent_phrase(phrase: str) -> AccentPhrase:
             base_index += 1
             continue
         for watch_index in range(base_index, len(phrase)):
-            if phrase[watch_index] == ACCENT_SYMBOL:
+            if phrase[watch_index] == _ACCENT_SYMBOL:
                 break
             # 普通の文字の場合
             stack += phrase[watch_index]
-            if stack in text2mora_with_unvoice:
+            if stack in _text2mora_with_unvoice:
                 matched_text = stack
         # push mora
         if matched_text is None:
             raise ParseKanaError(ParseKanaErrorCode.UNKNOWN_TEXT, text=stack)
         else:
-            moras.append(text2mora_with_unvoice[matched_text].copy(deep=True))
+            moras.append(_text2mora_with_unvoice[matched_text].copy(deep=True))
             base_index += len(matched_text)
             stack = ""
             matched_text = None
-        if outer_loop > LOOP_LIMIT:
+        if outer_loop > _LOOP_LIMIT:
             raise ParseKanaError(ParseKanaErrorCode.INFINITE_LOOP)
     if accent_index is None:
         raise ParseKanaError(ParseKanaErrorCode.ACCENT_NOTFOUND, text=phrase)
@@ -90,7 +90,7 @@ def parse_kana(text: str) -> List[AccentPhrase]:
         raise ParseKanaError(ParseKanaErrorCode.EMPTY_PHRASE, position=1)
 
     for i in range(len(text) + 1):
-        if i == len(text) or text[i] in [PAUSE_DELIMITER, NOPAUSE_DELIMITER]:
+        if i == len(text) or text[i] in [_PAUSE_DELIMITER, _NOPAUSE_DELIMITER]:
             phrase = text[phrase_base:i]
             if len(phrase) == 0:
                 raise ParseKanaError(
@@ -99,16 +99,16 @@ def parse_kana(text: str) -> List[AccentPhrase]:
                 )
             phrase_base = i + 1
 
-            is_interrogative = WIDE_INTERROGATION_MARK in phrase
+            is_interrogative = _WIDE_INTERROGATION_MARK in phrase
             if is_interrogative:
-                if WIDE_INTERROGATION_MARK in phrase[:-1]:
+                if _WIDE_INTERROGATION_MARK in phrase[:-1]:
                     raise ParseKanaError(
                         ParseKanaErrorCode.INTERROGATION_MARK_NOT_AT_END, text=phrase
                     )
-                phrase = phrase.replace(WIDE_INTERROGATION_MARK, "")
+                phrase = phrase.replace(_WIDE_INTERROGATION_MARK, "")
 
             accent_phrase: AccentPhrase = _text_to_accent_phrase(phrase)
-            if i < len(text) and text[i] == PAUSE_DELIMITER:
+            if i < len(text) and text[i] == _PAUSE_DELIMITER:
                 accent_phrase.pause_mora = Mora(
                     text="、",
                     consonant=None,
@@ -129,18 +129,18 @@ def create_kana(accent_phrases: List[AccentPhrase]) -> str:
     for i, phrase in enumerate(accent_phrases):
         for j, mora in enumerate(phrase.moras):
             if mora.vowel in ["A", "I", "U", "E", "O"]:
-                text += UNVOICE_SYMBOL
+                text += _UNVOICE_SYMBOL
 
             text += mora.text
             if j + 1 == phrase.accent:
-                text += ACCENT_SYMBOL
+                text += _ACCENT_SYMBOL
 
         if phrase.is_interrogative:
-            text += WIDE_INTERROGATION_MARK
+            text += _WIDE_INTERROGATION_MARK
 
         if i < len(accent_phrases) - 1:
             if phrase.pause_mora is None:
-                text += NOPAUSE_DELIMITER
+                text += _NOPAUSE_DELIMITER
             else:
-                text += PAUSE_DELIMITER
+                text += _PAUSE_DELIMITER
     return text