diff --git a/src/BacklogService.ts b/src/BacklogService.ts
index 6825cc9..53804cc 100644
--- a/src/BacklogService.ts
+++ b/src/BacklogService.ts
@@ -1,5 +1,5 @@
 import {BacklogClient, BacklogClientImpl, GoogleAppsScriptDateFormatter} from "./BacklogClient"
-import {Key, Project, Issue, BacklogDefinition, Locale, UserProperty, CustomFieldDefinition, IssueType} from "./datas"
+import {Key, Project, Issue, BacklogDefinition, Locale, UserProperty, CustomFieldDefinition, IssueType, isSupportedCustomField} from "./datas"
 import {HttpClient} from "./Http"
 import {Option, Some, None} from "./Option"
 import {Either, Right, Left} from "./Either"
@@ -45,7 +45,14 @@ export const getProject = (client: BacklogClient, key: Key<Project>, locale: Loc
 }
 
 const validate = (issues: List<any>, issueTypes: List<IssueType>, customFieldDefinitions: List<CustomFieldDefinition>, client: BacklogClient, locale: Locale): Either<Error, boolean> => {
-  const definitions = customFieldDefinitions.filter(item => item.typeId < 6)
+  for (let i = 0; i < customFieldDefinitions.length; i++) {
+    const definition = customFieldDefinitions[i]
+
+    if (definition.required && !isSupportedCustomField(definition))
+      return Left(Error(Message.VALIDATE_CUSTOM_FIELD_VALUE_IS_REQUIRED_UNSUPPORTED(definition.name, locale)))
+  }
+
+  const definitions = customFieldDefinitions.filter(item => isSupportedCustomField(item))
 
   for (let i = 0; i < issues.length; i++) {
     const issue = issues[i]
@@ -353,7 +360,7 @@ export const BacklogService = (spreadSheetService: SpreadSheetService): BacklogS
            */
           let customFieldName = ""
 
-          if (customField.typeId >= 6)
+          if (!isSupportedCustomField(customField))
             continue
           switch (customField.typeId) {
             case 1:
@@ -395,7 +402,7 @@ export const BacklogService = (spreadSheetService: SpreadSheetService): BacklogS
         let validationRuleIndex = 0
         for (let i = 0; i < definition.customFields.length; i++) {
           const customField = definition.customFields[i]
-          if (customField.typeId >= 6)
+          if (!isSupportedCustomField(customField))
             continue
           if (customField.typeId === 5) {
             definition.customFieldItemNames(customField).map(itemNames => {
diff --git a/src/datas.ts b/src/datas.ts
index f3a0560..da4e698 100644
--- a/src/datas.ts
+++ b/src/datas.ts
@@ -97,6 +97,9 @@ export interface CustomField extends WithId {
 }
 export const CustomField = (id: number, fieldTypeId: number, value: any) => ({id, fieldTypeId, value})
 
+export const isSupportedCustomField = (definition: CustomFieldDefinition) =>
+  definition.typeId < 6
+
 export interface BacklogDefinition {
   readonly issueTypes: List<IssueType>
   readonly categories: List<Category>
diff --git a/src/resources.ts b/src/resources.ts
index 073140f..7782be6 100644
--- a/src/resources.ts
+++ b/src/resources.ts
@@ -152,6 +152,13 @@ export const Message = {
     }
     return msg[locale]
   },
+  VALIDATE_CUSTOM_FIELD_VALUE_IS_REQUIRED_UNSUPPORTED: (definitionName: string, locale: Locale): string => {
+    const msg = {
+      "en": `Custom field value '${definitionName}' is required but it isn't supported. Please cancel this setting.`,
+      "ja": `カスタム属性 '${definitionName}' は必須ですがサポートされていません。必須の設定を解除してください。`
+    }
+    return msg[locale]
+  },
   VALIDATE_CUSTOM_FIELD_VALUE_IS_NUMBER: (definitionName: string, input: string, locale: Locale): string => {
     const msg = {
       "en": `Custom field value '${definitionName}' needs number. Row input: ${input}`,