diff --git a/src/qa_training/domain/service_make_features.py b/src/qa_training/domain/service_make_features.py
index f3d8280..003d973 100644
--- a/src/qa_training/domain/service_make_features.py
+++ b/src/qa_training/domain/service_make_features.py
@@ -52,7 +52,7 @@ def _make_y(
 
     def _handle_missing_values(self, df_customer_info) -> pd.DataFrame:
         """欠損値処理する."""
-        df_customer_info["Age"] = df_customer_info["Age"].fillna(10)
+        df_customer_info["Age"] = df_customer_info["Age"].fillna(20)
         df_customer_info["Cabin"] = df_customer_info["Cabin"].fillna("S")
         df_customer_info = df_customer_info.dropna()
         return df_customer_info
diff --git a/tests/qa_training/domain/service_make_features/missing_values/df_customer_info.csv b/tests/qa_training/domain/service_make_features/missing_values/df_customer_info.csv
new file mode 100644
index 0000000..7affe30
--- /dev/null
+++ b/tests/qa_training/domain/service_make_features/missing_values/df_customer_info.csv
@@ -0,0 +1,7 @@
+PassengerId,Survived,Pclass,Name,Sex,Age,SibSp,Parch,Ticket,Fare,Cabin,Embarked
+1,0,3,"Braund, Mr. Owen Harris",male,22,1,0,A/5 21171,7.25,C85,S
+2,1,1,"Cumings, Mrs. John Bradley (Florence Briggs Thayer)",female,38,1,0,PC 17599,71.2833,C85,C
+3,1,3,"Heikkinen, Miss. Laina",female,26,0,0,STON/O2. 3101282,7.925,C85,S
+4,1,1,"Futrelle, Mrs. Jacques Heath (Lily May Peel)",female,35,1,0,113803,53.1,C123,S
+5,0,3,"Allen, Mr. William Henry",male,35,0,0,373450,8.05,C85,S
+6,0,3,"Moran, Mr. James",male,,0,0,330877,8.4583,C85,Q
diff --git a/tests/qa_training/domain/service_make_features/missing_values/df_filled_expected.csv b/tests/qa_training/domain/service_make_features/missing_values/df_filled_expected.csv
new file mode 100644
index 0000000..6c539d2
--- /dev/null
+++ b/tests/qa_training/domain/service_make_features/missing_values/df_filled_expected.csv
@@ -0,0 +1,7 @@
+PassengerId,Survived,Pclass,Name,Sex,Age,SibSp,Parch,Ticket,Fare,Cabin,Embarked
+1,0,3,"Braund, Mr. Owen Harris",male,22,1,0,A/5 21171,7.25,C85,S
+2,1,1,"Cumings, Mrs. John Bradley (Florence Briggs Thayer)",female,38,1,0,PC 17599,71.2833,C85,C
+3,1,3,"Heikkinen, Miss. Laina",female,26,0,0,STON/O2. 3101282,7.925,C85,S
+4,1,1,"Futrelle, Mrs. Jacques Heath (Lily May Peel)",female,35,1,0,113803,53.1,C123,S
+5,0,3,"Allen, Mr. William Henry",male,35,0,0,373450,8.05,C85,S
+6,0,3,"Moran, Mr. James",male,20,0,0,330877,8.4583,C85,Q
diff --git a/tests/qa_training/domain/service_make_features/missing_values/test_missing_values_in_age.py b/tests/qa_training/domain/service_make_features/missing_values/test_missing_values_in_age.py
new file mode 100644
index 0000000..c23fc67
--- /dev/null
+++ b/tests/qa_training/domain/service_make_features/missing_values/test_missing_values_in_age.py
@@ -0,0 +1,27 @@
+
+
+
+import pandas as pd
+import pytest
+from qa_training.domain.service_make_features import ServiceMakeFeatures
+from qa_training.utils.my_assert_frame_equal import MyAssert
+
+
+@pytest.fixture()
+def fixture_run():
+    service = ServiceMakeFeatures()
+    df_customer_info = pd.read_csv("tests/qa_training/domain/service_make_features/missing_values/df_customer_info.csv")
+    df_filled_expected = pd.read_csv("tests/qa_training/domain/service_make_features/missing_values/df_filled_expected.csv")
+
+    return service, df_customer_info, df_filled_expected
+
+
+def test_run(fixture_run):
+    # Arrange
+    service, df_customer_info, df_filled_expected  = fixture_run
+
+    # Act
+    df_filled = service._handle_missing_values(df_customer_info=df_customer_info)
+
+    # Assert
+    MyAssert().assert_df(df_filled, df_filled_expected)
diff --git a/tests/qa_training/domain/test_service_make_features.py b/tests/qa_training/domain/test_service_make_features.py
deleted file mode 100644
index d5c0d8f..0000000
--- a/tests/qa_training/domain/test_service_make_features.py
+++ /dev/null
@@ -1,49 +0,0 @@
-import pandas as pd
-import pytest
-from qa_training.domain.service_make_features import ServiceMakeFeatures
-from qa_training.utils.my_assert_frame_equal import MyAssert
-
-
-@pytest.fixture
-def fixture_run():
-    service_make_features = ServiceMakeFeatures()
-
-    df_customer_info = pd.read_csv(
-        "tests/common_data/df_customer_info.csv",
-    )
-    df_id_expected = pd.read_csv(
-        "tests/common_data/df_id.csv",
-    )
-    df_X_expected = pd.read_csv(
-        "tests/common_data/df_X.csv",
-    )
-    df_y_expected = pd.read_csv(
-        "tests/common_data/df_y.csv",
-    )
-    return (
-        service_make_features,
-        df_customer_info,
-        df_id_expected,
-        df_X_expected,
-        df_y_expected,
-    )
-
-
-def test_run(
-    fixture_run: tuple[
-        ServiceMakeFeatures, pd.DataFrame, pd.DataFrame, pd.DataFrame, pd.DataFrame
-    ]
-):
-    (
-        service_make_features,
-        df_customer_info,
-        df_id_expected,
-        df_X_expected,
-        df_y_expected,
-    ) = fixture_run
-
-    df_id, df_X, df_y = service_make_features.run(df_customer_info)
-
-    MyAssert().assert_df(df_id, df_id_expected)
-    MyAssert().assert_df(df_X, df_X_expected)
-    MyAssert().assert_df(df_y, df_y_expected)