diff --git a/src/tutorial.py b/src/tutorial.py
index 54dc3d1..f847ab2 100644
--- a/src/tutorial.py
+++ b/src/tutorial.py
@@ -36,3 +36,22 @@ def convert_to_decimal_number(cls, num: int):
         for i in range(len(n)):
             result += int(n[i]) * (2 ** (len(n) - i - 1))
         return result
+
+    @classmethod
+    def binary_search(cls, values: list[int], target: int):
+        left = 0
+        right = len(values) - 1
+        answer = -1
+
+        while left <= right:
+            middle = (left + right) // 2
+            if values[middle] == target:
+                answer = middle
+                right = middle - 1
+                continue
+            if values[middle] < target:
+                left = middle + 1
+            else:
+                right = middle - 1
+
+        return answer
diff --git a/test/test_binary_search.py b/test/test_binary_search.py
new file mode 100644
index 0000000..73c9a01
--- /dev/null
+++ b/test/test_binary_search.py
@@ -0,0 +1,46 @@
+import unittest
+from src.tutorial import Tutorial
+
+
+class TestBinarySearch(unittest.TestCase):
+    def test_binary_search_found_middle(self):
+        self.assertEqual(
+            Tutorial.binary_search([1, 3, 5, 7, 9], 5),
+            2,
+            '中央の要素が見つかる'
+        )
+
+    def test_binary_search_found_first(self):
+        self.assertEqual(
+            Tutorial.binary_search([1, 3, 5, 7, 9], 1),
+            0,
+            '先頭の要素が見つかる'
+        )
+
+    def test_binary_search_found_last(self):
+        self.assertEqual(
+            Tutorial.binary_search([1, 3, 5, 7, 9], 9),
+            4,
+            '末尾の要素が見つかる'
+        )
+
+    def test_binary_search_not_found(self):
+        self.assertEqual(
+            Tutorial.binary_search([1, 3, 5, 7, 9], 4),
+            -1,
+            '存在しない要素は-1を返す'
+        )
+
+    def test_binary_search_duplicate_values(self):
+        self.assertEqual(
+            Tutorial.binary_search([1, 2, 2, 2, 3], 2),
+            1,
+            '重複要素は左端のindexを返す'
+        )
+
+    def test_binary_search_empty_array(self):
+        self.assertEqual(
+            Tutorial.binary_search([], 1),
+            -1,
+            '空配列では-1を返す'
+        )