diff --git a/optuna_dashboard/ts/apiClient.ts b/optuna_dashboard/ts/apiClient.ts
index d50cd938..d364b676 100644
--- a/optuna_dashboard/ts/apiClient.ts
+++ b/optuna_dashboard/ts/apiClient.ts
@@ -445,11 +445,14 @@ type PlotResponse = {
   data: plotly.Data[]
   layout: plotly.Layout
 }
+export enum PlotType {
+  Contour = "contour",
+}
 export const getPlotAPI = (
   studyId: number,
-  plotName: string
+  plotType: PlotType
 ): Promise<PlotResponse> => {
   return axiosInstance
-    .get<PlotResponse>(`/api/studies/${studyId}/plot/${plotName}`)
+    .get<PlotResponse>(`/api/studies/${studyId}/plot/${plotType}`)
     .then<PlotResponse>((res) => res.data)
 }
diff --git a/optuna_dashboard/ts/components/GraphContour.tsx b/optuna_dashboard/ts/components/GraphContour.tsx
index b6ab313e..d7c05d3f 100644
--- a/optuna_dashboard/ts/components/GraphContour.tsx
+++ b/optuna_dashboard/ts/components/GraphContour.tsx
@@ -16,7 +16,7 @@ import { plotlyDarkTemplate } from "./PlotlyDarkMode"
 import { useMergedUnionSearchSpace } from "../searchSpace"
 import { getAxisInfo } from "../graphUtil"
 import { useQuery } from "../urlQuery"
-import { getPlotAPI } from "../apiClient"
+import { getPlotAPI, PlotType } from "../apiClient"
 
 const plotDomId = "graph-contour"
 
@@ -39,7 +39,7 @@ const ContourBackend: FC<{
     if (studyId === undefined) {
       return
     }
-    getPlotAPI(studyId, "contour")
+    getPlotAPI(studyId, PlotType.Contour)
       .then(({ data, layout }) => {
         plotly.react(plotDomId, data, layout)
       })