diff --git a/src/components/contest/Contest.vue b/src/components/contest/Contest.vue
index b8ada42..3688db4 100644
--- a/src/components/contest/Contest.vue
+++ b/src/components/contest/Contest.vue
@@ -11,6 +11,14 @@
                   <span class="is-size-5 has-text-weight-bold">
                     期間: {{formatDate(startAt)}} ~ {{formatDate(endAt)}}<br>
                   </span>
+                  <span
+                    v-if="isFlexibleContest && isEntered"
+                    class="is-size-5 has-text-weight-bold"
+                  >
+                    あなたのコンテスト時間:
+                    {{formatDate(flexibleCreatedAt)}} ~
+                    {{formatDate(flexibleEndAt)}}<br>
+                  </span>
                   <span class="is-size-7">
                     作成日時: {{formatDate(createdAt)}}<br>
                     最終更新: {{formatDate(updatedAt)}}
@@ -19,8 +27,15 @@
               </div>
             </div>
             <div class="navbar-end">
-              <span v-if="canEnter && !isEntered && problems === null" class="navbar-item">
-                <button @click="enter" class="button is-large is-outlined">
+              <span
+                v-if="enterable"
+                class="navbar-item"
+              >
+                <button
+                  @click="myEnter"
+                  class="button is-large is-outlined"
+                  :disabled="this.isFlexibleContest && this.countDownTimer !== 'Already started'"
+                >
                   コンテストに参加する
                 </button>
               </span>
@@ -67,6 +82,10 @@
       </article>
     </div>
     <div class="container">
+      <EnterConfirmationModal
+        :isActive="showConfirmationModal"
+        @close="showConfirmationModal = false"
+      />
       <ErrorNotification :error="error"/>
       <template v-if="problems !== null">
         <div class="columns is-mobile" v-if="problems.length !== 0">
@@ -187,6 +206,7 @@ import ErrorNotification from '@/components/common/ErrorNotification';
 import Modal from '@/components/common/Modal';
 import SubmitModal from '@/components/problem/SubmitModal';
 import ResultModal from './result_modal/ResultModal';
+import EnterConfirmationModal from './EnterConfirmationModal';
 
 import Tag from './Tag';
 
@@ -198,6 +218,7 @@ export default {
       showStandingsModal: false,
       showResultListModal: false,
       showSubmitModal: false,
+      showConfirmationModal: false,
       activeTab: 0,
       diff: 300000,
     };
@@ -216,6 +237,8 @@ export default {
       'participants',
       'id',
       'error',
+      'duration',
+      'flexibleCreatedAt',
     ]),
     ...mapState('koneko/timeDiff', [
       'timeDiff',
@@ -224,7 +247,15 @@ export default {
       'canEnter',
       'isEntered',
       'isWriter',
+      'isFlexibleContest',
+      'flexibleEndAt',
     ]),
+    enterable() {
+      return this.canEnter &&
+        !this.isEntered &&
+        this.problems === null
+      ;
+    },
     countDownTimer() {
       if (this.diff < 0) return 'Already started';
       const DD = `00${Math.floor(this.diff / 1000 / 60 / 60 / 24)}`.slice(-2);
@@ -284,6 +315,13 @@ export default {
       await this.getResults();
       this.showResultListModal = true;
     },
+    myEnter() {
+      if (this.isFlexibleContest) {
+        this.showConfirmationModal = true;
+      } else {
+        this.enter();
+      }
+    },
     num2alpha(num) {
       return String.fromCharCode(97 + num);
     },
@@ -308,6 +346,7 @@ export default {
     Tag,
     Modal,
     Problem,
+    EnterConfirmationModal,
     ErrorNotification,
     SubmitModal,
     ResultModal,
diff --git a/src/components/contest/EnterConfirmationModal.vue b/src/components/contest/EnterConfirmationModal.vue
new file mode 100644
index 0000000..35057eb
--- /dev/null
+++ b/src/components/contest/EnterConfirmationModal.vue
@@ -0,0 +1,49 @@
+<template>
+  <Modal
+    :isActive="isActive"
+    title="参加確認"
+    @close="close"
+  >
+    <p>
+      参加するとすぐにコンテストが始まります。<br/>
+      コンテスト時間は、参加から{{Math.floor(duration / 60)}}分です
+    </p>
+    <div slot="footer">
+      <button class="button is-success" @click="myEnter">参加する</button>
+      <button class="button" @click="close">キャンセル</button>
+   </div>
+   </Modal>
+</template>
+
+<script>
+import { mapActions, mapState } from 'vuex';
+import Modal from '@/components/common/Modal';
+
+export default {
+  props: [
+    'isActive',
+  ],
+  computed: {
+    ...mapState('koneko/contests', [
+      'duration',
+      'id',
+    ]),
+  },
+  methods: {
+    ...mapActions('koneko/contests', [
+      'enter',
+      'getContest',
+    ]),
+    async myEnter() {
+      await this.enter();
+      this.$emit('close');
+    },
+    close() {
+      this.$emit('close');
+    },
+  },
+  components: {
+    Modal,
+  },
+};
+</script>
diff --git a/src/store/modules/contests/index.js b/src/store/modules/contests/index.js
index 3745799..e195951 100644
--- a/src/store/modules/contests/index.js
+++ b/src/store/modules/contests/index.js
@@ -19,6 +19,8 @@ export default {
     requiredWatching: false,
     isWaitingJudge: true,
     error: null,
+    duration: null,
+    flexibleCreatedAt: null,
   },
   getters: {
     isWriter({ writers }, _, rootState) {
@@ -30,6 +32,15 @@ export default {
     canEnter(_, { isWriter, isEntered }) {
       return !isEntered && !isWriter;
     },
+    isFlexibleContest({ duration }) {
+      return !!duration;
+    },
+    flexibleEndAt({ flexibleCreatedAt, duration }) {
+      if (flexibleCreatedAt === null) return null;
+      const tmp = new Date(flexibleCreatedAt);
+      tmp.setSeconds(tmp.getSeconds() + duration);
+      return tmp;
+    },
   },
   mutations: {
     setContestData(state, contestData) {
@@ -48,8 +59,9 @@ export default {
         name: v.name, displayName: v.displayName, id: v.id,
       }));
       state.participants = contestData.participants.map(v => ({
-        name: v.name, displayName: v.displayName, id: v.id,
+        name: v.user.name, displayName: v.user.displayName, id: v.user.id,
       }));
+      state.duration = contestData.duration ? contestData.duration / 1000000000 : null;
     },
     setStatusesWatcherFlag(state) {
       state.statusesWatcherFlag = true;
@@ -73,12 +85,15 @@ export default {
       });
       state.isWaitingJudge = state.problems.some(({ status }) => status < 2 && status > -1);
     },
+    setFlexibleCreatedAt(state, createdAt) {
+      state.flexibleCreatedAt = createdAt;
+    },
     waitJudge(state) {
       state.isWaitingJudge = true;
     },
     setParticipants(state, participants) {
       state.participants = participants.map(v => ({
-        name: v.name, displayName: v.displayName, id: v.id,
+        name: v.user.name, displayName: v.user.displayName, id: v.user.id,
       }));
     },
     setError(state, error) {
@@ -86,10 +101,18 @@ export default {
     },
   },
   actions: {
-    async getContest({ commit, rootState }, contestID) {
+    async getContest({ state, commit, rootState }, contestID) {
       try {
         const res = await api.getContest(rootState.koneko.sessionID, contestID);
         commit('setContestData', res.data);
+        if (state.duration) {
+          for (let i = 0; i < res.data.participants.length; i += 1) {
+            if (rootState.koneko.user.id === res.data.participants[i].user.id) {
+              commit('setFlexibleCreatedAt', new Date(res.data.participants[i].createdAt));
+              break;
+            }
+          }
+        }
         commit('setRequiredWatching', true);
       } catch (e) {
         commit('setError', e);
@@ -128,6 +151,14 @@ export default {
       try {
         const res = await api.enterContest(rootState.koneko.sessionID, state.id);
         commit('setParticipants', res.data.participants);
+        if (state.duration) {
+          for (let i = 0; i < res.data.participants.length; i += 1) {
+            if (rootState.koneko.user.id === res.data.participants[i].user.id) {
+              commit('setFlexibleCreatedAt', new Date(res.data.participants[i].createdAt));
+              break;
+            }
+          }
+        }
       } catch (e) {
         commit('setError', e);
       }