diff --git a/src/rmqrcode/encoder/alphanumeric_encoder.py b/src/rmqrcode/encoder/alphanumeric_encoder.py
index 2a0839f..3e30746 100644
--- a/src/rmqrcode/encoder/alphanumeric_encoder.py
+++ b/src/rmqrcode/encoder/alphanumeric_encoder.py
@@ -89,4 +89,4 @@ def characters_num(cls, data):
 
     @classmethod
     def is_valid_characters(cls, data):
-        return bool(re.match(r"^[0-9A-Z\s\$\%\*\+\-\.\/\:]*$", data))
+        return all((char in cls.CHARACTER_MAP.keys() for char in data))
diff --git a/src/rmqrcode/encoder/kanji_encoder.py b/src/rmqrcode/encoder/kanji_encoder.py
index ba5fc65..4b8c464 100644
--- a/src/rmqrcode/encoder/kanji_encoder.py
+++ b/src/rmqrcode/encoder/kanji_encoder.py
@@ -13,9 +13,9 @@ def _encoded_bits(cls, data):
             shift_jis = c.encode("shift-jis")
             hex_value = shift_jis[0] * 256 + shift_jis[1]
 
-            if hex_value >= 0x8140 and hex_value <= 0x9FFC:
+            if 0x8140 <= hex_value <= 0x9FFC:
                 sub = 0x8140
-            elif hex_value >= 0xE040 and hex_value <= 0xEBBF:
+            elif 0xE040 <= hex_value <= 0xEBBF:
                 sub = 0xC140
             else:
                 raise IllegalCharacterError()
@@ -44,6 +44,6 @@ def is_valid_characters(cls, data):
             if len(shift_jis) < 2:
                 return False
             hex_value = shift_jis[0] * 256 + shift_jis[1]
-            if (0x8140 > hex_value and 0x9FFC < hex_value) or (0xE040 > hex_value and 0xEBBF < hex_value):
+            if hex_value < 0x8140 or 0x9FFC < hex_value < 0xE040 or 0xEBBF < hex_value:
                 return False
         return True
diff --git a/src/rmqrcode/encoder/numeric_encoder.py b/src/rmqrcode/encoder/numeric_encoder.py
index 208e7f5..1830300 100644
--- a/src/rmqrcode/encoder/numeric_encoder.py
+++ b/src/rmqrcode/encoder/numeric_encoder.py
@@ -45,4 +45,4 @@ def characters_num(cls, data):
 
     @classmethod
     def is_valid_characters(cls, data):
-        return bool(re.match(r"^[0-9]*$", data))
+        return all((char in "0123456789" for char in data))