diff --git a/plugin/filter/render.go b/plugin/filter/render.go
index 0bd8fdb60..9d3bc60af 100644
--- a/plugin/filter/render.go
+++ b/plugin/filter/render.go
@@ -207,6 +207,17 @@ func (r *renderer) renderScalarComparison(field Field, op ComparisonOperator, ri
 	}
 
 	columnExpr := field.columnExpr(r.dialect)
+	if lit == nil {
+		switch op {
+		case CompareEq:
+			return renderResult{sql: fmt.Sprintf("%s IS NULL", columnExpr)}, nil
+		case CompareNeq:
+			return renderResult{sql: fmt.Sprintf("%s IS NOT NULL", columnExpr)}, nil
+		default:
+			return renderResult{}, errors.Errorf("operator %s not supported for null comparison", op)
+		}
+	}
+
 	placeholder := ""
 	switch field.Type {
 	case FieldTypeString:
diff --git a/plugin/filter/schema.go b/plugin/filter/schema.go
index 8cfd2d915..c172eb62a 100644
--- a/plugin/filter/schema.go
+++ b/plugin/filter/schema.go
@@ -297,7 +297,7 @@ func NewAttachmentSchema() Schema {
 		cel.Variable("filename", cel.StringType),
 		cel.Variable("mime_type", cel.StringType),
 		cel.Variable("create_time", cel.IntType),
-		cel.Variable("memo_id", cel.IntType),
+		cel.Variable("memo_id", cel.AnyType),
 		nowFunction,
 	}
 
diff --git a/store/test/attachment_filter_test.go b/store/test/attachment_filter_test.go
index a46d31a82..3ae64b024 100644
--- a/store/test/attachment_filter_test.go
+++ b/store/test/attachment_filter_test.go
@@ -328,9 +328,18 @@ func TestAttachmentFilterNullMemoId(t *testing.T) {
 	tc.CreateAttachment(NewAttachmentBuilder(tc.CreatorID).Filename("with_memo.png").MimeType("image/png").MemoID(&memo.ID))
 	tc.CreateAttachment(NewAttachmentBuilder(tc.CreatorID).Filename("no_memo.png").MimeType("image/png"))
 
-	attachments := tc.ListWithFilter(`memo_id == ` + formatInt32(memo.ID))
+	// Test: memo_id == null
+	attachments := tc.ListWithFilter(`memo_id == null`)
+	require.Len(t, attachments, 1)
+	require.Equal(t, "no_memo.png", attachments[0].Filename)
+	require.Nil(t, attachments[0].MemoID)
+
+	// Test: memo_id != null
+	attachments = tc.ListWithFilter(`memo_id != null`)
 	require.Len(t, attachments, 1)
 	require.Equal(t, "with_memo.png", attachments[0].Filename)
+	require.NotNil(t, attachments[0].MemoID)
+	require.Equal(t, memo.ID, *attachments[0].MemoID)
 }
 
 func TestAttachmentFilterEmptyFilename(t *testing.T) {
diff --git a/web/src/pages/Attachments.tsx b/web/src/pages/Attachments.tsx
index 21be4edb4..ae4f37af2 100644
--- a/web/src/pages/Attachments.tsx
+++ b/web/src/pages/Attachments.tsx
@@ -156,7 +156,19 @@ const Attachments = () => {
   // Delete all unused attachments
   const handleDeleteUnusedAttachments = useCallback(async () => {
     try {
-      await Promise.all(unusedAttachments.map((attachment) => deleteAttachment(attachment.name)));
+      let allUnusedAttachments: Attachment[] = [];
+      let nextPageToken = "";
+      do {
+        const response = await attachmentServiceClient.listAttachments({
+          pageSize: 1000,
+          pageToken: nextPageToken,
+          filter: "memo_id == null",
+        });
+        allUnusedAttachments = [...allUnusedAttachments, ...response.attachments];
+        nextPageToken = response.nextPageToken;
+      } while (nextPageToken);
+
+      await Promise.all(allUnusedAttachments.map((attachment) => deleteAttachment(attachment.name)));
       toast.success(t("resource.delete-all-unused-success"));
     } catch (error) {
       handleError(error, toast.error, {
@@ -166,7 +178,7 @@ const Attachments = () => {
     } finally {
       await handleRefetch();
     }
-  }, [unusedAttachments, t, handleRefetch, deleteAttachment]);
+  }, [t, handleRefetch, deleteAttachment]);
 
   // Handle search input change
   const handleSearchChange = useCallback((e: React.ChangeEvent<HTMLInputElement>) => {