diff --git a/test/test_synthesis_engine.py b/test/test_synthesis_engine.py
index c01ea15cc..17f0ed4a5 100644
--- a/test/test_synthesis_engine.py
+++ b/test/test_synthesis_engine.py
@@ -179,9 +179,9 @@ def test_pad_with_silence():
 
     # Expects
     true_moras_with_silence = [
-        _gen_mora(" ", None, None, "sil", 2 * 0.01067, 0.0),
+        _gen_mora("　", None, None, "sil", 2 * 0.01067, 0.0),
         _gen_mora("ヒ", "h", 2 * 0.01067, "i", 4 * 0.01067, 100.0),
-        _gen_mora(" ", None, None, "sil", 6 * 0.01067, 0.0),
+        _gen_mora("　", None, None, "sil", 6 * 0.01067, 0.0),
     ]
 
     # Outputs
@@ -195,13 +195,13 @@ def test_calc_frame_per_phoneme():
     # Inputs
     query = _gen_query(speedScale=2.0)
     moras = [
-        _gen_mora(" ", None, None, " ", 2 * 0.01067, 0.0),  # 0.01067 [sec/frame]
+        _gen_mora("　", None, None, "　", 2 * 0.01067, 0.0),  # 0.01067 [sec/frame]
         _gen_mora("コ", "k", 2 * 0.01067, "o", 4 * 0.01067, 0.0),
         _gen_mora("ン", None, None, "N", 4 * 0.01067, 0.0),
         _gen_mora("、", None, None, "pau", 2 * 0.01067, 0.0),
         _gen_mora("ヒ", "h", 2 * 0.01067, "i", 4 * 0.01067, 0.0),
         _gen_mora("ホ", "h", 4 * 0.01067, "O", 2 * 0.01067, 0.0),
-        _gen_mora(" ", None, None, " ", 6 * 0.01067, 0.0),
+        _gen_mora("　", None, None, "　", 6 * 0.01067, 0.0),
     ]
 
     # Expects
@@ -220,13 +220,13 @@ def test_calc_frame_pitch():
     # Inputs
     query = _gen_query(pitchScale=2.0, intonationScale=0.5)
     moras = [
-        _gen_mora(" ", None, None, " ", 0.0, 0.0),
+        _gen_mora("　", None, None, "　", 0.0, 0.0),
         _gen_mora("コ", "k", 0.0, "o", 0.0, 50.0),
         _gen_mora("ン", None, None, "N", 0.0, 50.0),
         _gen_mora("、", None, None, "pau", 0.0, 0.0),
         _gen_mora("ヒ", "h", 0.0, "i", 0.0, 125.0),
         _gen_mora("ホ", "h", 0.0, "O", 0.0, 0.0),
-        _gen_mora(" ", None, None, " ", 0.0, 0.0),
+        _gen_mora("　", None, None, "　", 0.0, 0.0),
     ]
     phoneme_str = "pau k o N pau h i h O pau"
     phonemes = [OjtPhoneme(p, 0, 0) for p in phoneme_str.split()]
diff --git a/voicevox_engine/synthesis_engine/synthesis_engine.py b/voicevox_engine/synthesis_engine/synthesis_engine.py
index bd6e5d73f..9673e0742 100644
--- a/voicevox_engine/synthesis_engine/synthesis_engine.py
+++ b/voicevox_engine/synthesis_engine/synthesis_engine.py
@@ -89,9 +89,9 @@ def pre_process(
     Returns
     -------
     flatten_moras : List[Mora]
-        モーラ時系列（前後の無音含まない）
+        モーラ列（前後の無音含まない）
     phoneme_data_list : List[OjtPhoneme]
-        音素時系列（前後の無音含む）
+        音素列（前後の無音含む）
     """
     flatten_moras = to_flatten_moras(accent_phrases)
 
@@ -112,7 +112,7 @@ def pre_process(
 
 def generate_silence_mora(length: float) -> Mora:
     """無音モーラの生成"""
-    return Mora(text=" ", vowel="sil", vowel_length=length, pitch=0.0)
+    return Mora(text="　", vowel="sil", vowel_length=length, pitch=0.0)
 
 
 def pad_with_silence(moras: list[Mora], query: AudioQuery) -> list[Mora]: