diff --git a/internal/function_timestamp.go b/internal/function_timestamp.go
index c851dad..c088d1d 100644
--- a/internal/function_timestamp.go
+++ b/internal/function_timestamp.go
@@ -125,26 +125,25 @@ func TIMESTAMP_TRUNC(t time.Time, part, zone string) (Value, error) {
 	case "MICROSECOND":
 		return TimestampValue(t), nil
 	case "MILLISECOND":
-		sec := time.Duration(t.Second()) - time.Duration(t.Second())/time.Microsecond
+		nsec := (t.Nanosecond() / int(time.Millisecond)) * int(time.Millisecond)
 		return TimestampValue(time.Date(
 			t.Year(),
 			t.Month(),
 			t.Day(),
 			t.Hour(),
 			t.Minute(),
-			int(sec),
-			0,
+			t.Second(),
+			nsec,
 			loc,
 		)), nil
 	case "SECOND":
-		sec := time.Duration(t.Second()) / time.Second
 		return TimestampValue(time.Date(
 			t.Year(),
 			t.Month(),
 			t.Day(),
 			t.Hour(),
 			t.Minute(),
-			int(sec),
+			t.Second(),
 			0,
 			loc,
 		)), nil
diff --git a/internal/function_timestamp_test.go b/internal/function_timestamp_test.go
new file mode 100644
index 0000000..e6ccbd4
--- /dev/null
+++ b/internal/function_timestamp_test.go
@@ -0,0 +1,94 @@
+package internal_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/goccy/go-zetasqlite/internal"
+)
+
+func Test_TIMESTAMP_TRUNC(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		input    time.Time
+		part     string
+		expected time.Time
+		isErr    bool
+	}{
+		{
+			input:    mustParseTime(t, "2024-06-28T08:24:31.123456Z"),
+			part:     "MICROSECOND",
+			expected: mustParseTime(t, "2024-06-28T08:24:31.123456Z"),
+			isErr:    false,
+		},
+		{
+			input:    mustParseTime(t, "2024-06-28T08:24:31.123456Z"),
+			part:     "MILLISECOND",
+			expected: mustParseTime(t, "2024-06-28T08:24:31.123Z"),
+			isErr:    false,
+		},
+		{
+			input:    mustParseTime(t, "2024-06-28T08:24:31.123456Z"),
+			part:     "SECOND",
+			expected: mustParseTime(t, "2024-06-28T08:24:31.0Z"),
+			isErr:    false,
+		},
+		{
+			input:    mustParseTime(t, "2024-06-28T08:24:31.123456Z"),
+			part:     "MINUTE",
+			expected: mustParseTime(t, "2024-06-28T08:24:00.0Z"),
+			isErr:    false,
+		},
+		{
+			input:    mustParseTime(t, "2024-06-28T08:24:31.123456Z"),
+			part:     "HOUR",
+			expected: mustParseTime(t, "2024-06-28T08:00:00.0Z"),
+			isErr:    false,
+		},
+		{
+			input:    mustParseTime(t, "2024-06-28T08:24:31.123456Z"),
+			part:     "INVALID_PART",
+			expected: mustParseTime(t, "2024-06-28T00:00:00.0Z"),
+			isErr:    true,
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+
+		t.Run(tc.part, func(t *testing.T) {
+			t.Parallel()
+
+			res, err := internal.TIMESTAMP_TRUNC(tc.input, tc.part, "")
+
+			if err != nil {
+				if !tc.isErr {
+					t.Fatal("unexpected err", err)
+				}
+
+				return
+			}
+			if tc.isErr {
+				t.Fatal("expected err, got nil")
+			}
+
+			resTime, err := res.ToTime()
+			if err != nil {
+				t.Fatal(err)
+			}
+			if resTime != tc.expected {
+				t.Fatalf("result %s not equal %v", resTime, tc.expected)
+			}
+		})
+	}
+}
+
+func mustParseTime(t *testing.T, str string) time.Time {
+	res, err := time.Parse(time.RFC3339Nano, str)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return res
+}