diff --git a/.github/workflows/backend-ci.yml b/.github/workflows/backend-ci.yml
new file mode 100644
index 0000000..1eaa9cd
--- /dev/null
+++ b/.github/workflows/backend-ci.yml
@@ -0,0 +1,53 @@
+name: Server CI
+
+on:
+  pull_request:
+    paths:
+      - 'server/**'
+      - '.github/workflows/backend-ci.yml'
+
+env:
+  GO_VERSION: '1.24.4'
+
+defaults:
+  run:
+    working-directory: server/src
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+   lint-test-and-build:
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    permissions:
+      checks: write
+      contents: read
+      pull-requests: write
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Go
+        uses: actions/setup-go@v6
+        with:
+          go-version: ${{ env.GO_VERSION }}
+
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v8
+        with:
+          version: v2.1
+          working-directory: server/src
+
+      - name: Check formatting
+        run: |
+          fmt=$(gofmt -l .)
+          if [ -n "$fmt" ]; then
+            echo "Go files not formatted:"
+            echo "$fmt"
+            exit 1
+          fi
+
+      - name: Build
+        run: go build cmd/route/main.go
diff --git a/server/src/cmd/route/main.go b/server/src/cmd/route/main.go
index 1243597..4d68c92 100644
--- a/server/src/cmd/route/main.go
+++ b/server/src/cmd/route/main.go
@@ -39,9 +39,9 @@ func main() {
 
 	api := e.Group("/api")
 
-    api.GET("/", func(c echo.Context) error {
-        return c.String(200, "OK")
-    })
+	api.GET("/", func(c echo.Context) error {
+		return c.String(200, "OK")
+	})
 	room.RegisterRoutes(api.Group("/room"), db)
 	// quiz.RegisterRoutes に quizSvc を渡す
 	quiz.RegisterRoutes(api.Group("/quiz"), hub, quizSvc)
diff --git a/server/src/config/config.go b/server/src/config/config.go
index d2c532e..4bdcbc7 100644
--- a/server/src/config/config.go
+++ b/server/src/config/config.go
@@ -1,4 +1,3 @@
-
 package config
 
 import (
diff --git a/server/src/internal/database/database.go b/server/src/internal/database/database.go
index 59be438..05fe7dc 100644
--- a/server/src/internal/database/database.go
+++ b/server/src/internal/database/database.go
@@ -8,8 +8,8 @@ import (
 
 	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/aws/aws-sdk-go-v2/config"
-	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
 	"github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue"
+	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
 	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
 	roomtypes "server/src/internal/feature/room/types"
 )
@@ -33,15 +33,12 @@ func NewDBConnection() (*DBHandler, error) {
 		tableName = "quiz" // デフォルト名
 	}
 
-	tableName = "quiz"
-
 	return &DBHandler{
 		client:    client,
 		tableName: tableName,
 	}, nil
 }
 
-
 // ルームを1件取得
 func (h *DBHandler) ReadDB(id string) (*roomtypes.Room, error) {
 	resp, err := h.client.GetItem(context.TODO(), &dynamodb.GetItemInput{
@@ -80,7 +77,6 @@ func (h *DBHandler) WriteDB(room *roomtypes.Room) error {
 	return err
 }
 
-
 func (h *DBHandler) DeleteRoom(roomID string) error {
 	_, err := h.client.DeleteItem(context.TODO(), &dynamodb.DeleteItemInput{
 		TableName: aws.String(h.tableName),
diff --git a/server/src/internal/feature/quiz/handler/quizHandler.go b/server/src/internal/feature/quiz/handler/quizHandler.go
index 8b0c37d..1c232ee 100644
--- a/server/src/internal/feature/quiz/handler/quizHandler.go
+++ b/server/src/internal/feature/quiz/handler/quizHandler.go
@@ -2,12 +2,12 @@
 package handler
 
 import (
+	ws "github.com/gorilla/websocket"
+	"github.com/labstack/echo/v4"
 	"log"
 	"net/http"
 	"server/src/internal/feature/quiz/service"
 	"server/src/internal/feature/quiz/websocket"
-	ws "github.com/gorilla/websocket"
-	"github.com/labstack/echo/v4"
 )
 
 var upgrader = ws.Upgrader{
diff --git a/server/src/internal/feature/quiz/service/quizService.go b/server/src/internal/feature/quiz/service/quizService.go
index dddc716..153eaa8 100644
--- a/server/src/internal/feature/quiz/service/quizService.go
+++ b/server/src/internal/feature/quiz/service/quizService.go
@@ -155,7 +155,7 @@ func (s *QuizService) nextQuestion(roomID string) {
 	}
 
 	state.QuestionNumber++
-	
+
 	// 重複を避けて問題を選択
 	nextQuestion := s.getNextUniqueQuestion(state.UsedQuestionIDs)
 	if nextQuestion == nil {
@@ -163,7 +163,7 @@ func (s *QuizService) nextQuestion(roomID string) {
 		s.endGame(roomID)
 		return
 	}
-	
+
 	state.CurrentQuestion = nextQuestion
 	state.UsedQuestionIDs = append(state.UsedQuestionIDs, nextQuestion.ID)
 	state.AnsweredUsers = make(map[string]bool)
@@ -228,15 +228,14 @@ func (s *QuizService) endGame(roomID string) {
 	log.Printf("Game ended in room %s", roomID)
 }
 
-
 // getNextUniqueQuestion は出題済みでない問題を返します。
 func (s *QuizService) getNextUniqueQuestion(usedIDs []string) *types.Question {
 	availableQuestions := make([]*types.Question, 0)
-	
+
 	for i := range s.questions {
 		question := &s.questions[i]
 		isUsed := false
-		
+
 		// 出題済みかどうかチェック
 		for _, usedID := range usedIDs {
 			if question.ID == usedID {
@@ -244,27 +243,20 @@ func (s *QuizService) getNextUniqueQuestion(usedIDs []string) *types.Question {
 				break
 			}
 		}
-		
+
 		if !isUsed {
 			availableQuestions = append(availableQuestions, question)
 		}
 	}
-	
+
 	if len(availableQuestions) == 0 {
 		return nil // 出題可能な問題がない
 	}
-	
+
 	// 出題可能な問題からランダム選択
 	return availableQuestions[rand.Intn(len(availableQuestions))]
 }
 
-func (s *QuizService) getRandomQuestion() *types.Question {
-	if len(s.questions) == 0 {
-		return nil
-	}
-	return &s.questions[rand.Intn(len(s.questions))]
-}
-
 func loadQuestions(filePath string) ([]types.Question, error) {
 	file, err := os.ReadFile(filePath)
 	if err != nil {
diff --git a/server/src/internal/feature/quiz/types/quizType.go b/server/src/internal/feature/quiz/types/quizType.go
index ca7d309..41158cc 100644
--- a/server/src/internal/feature/quiz/types/quizType.go
+++ b/server/src/internal/feature/quiz/types/quizType.go
@@ -6,7 +6,7 @@ type Message struct {
 	Type    string      `json:"type"`
 	Payload interface{} `json:"payload,omitempty"`
 	// RoomID はJSONには含めず、ハブ内部でのルーティングに使用します。
-	RoomID  string      `json:"-"`
+	RoomID string `json:"-"`
 }
 
 // Question は1つのクイズ問題を表す構造体です。
@@ -29,8 +29,8 @@ type GameState struct {
 
 // PlayerResult は最終結果のランキング表示に使用する構造体です。
 type PlayerResult struct {
-	UserID   string `json:"userId"`
+	UserID string `json:"userId"`
 	// Name     string `json:"name"` // 必要であればユーザー名も追加
-	Score    int    `json:"score"`
-	Rank     int    `json:"rank"`
+	Score int `json:"score"`
+	Rank  int `json:"rank"`
 }
diff --git a/server/src/internal/feature/quiz/websocket/client.go b/server/src/internal/feature/quiz/websocket/client.go
index 855de94..9ad3f0e 100644
--- a/server/src/internal/feature/quiz/websocket/client.go
+++ b/server/src/internal/feature/quiz/websocket/client.go
@@ -2,9 +2,9 @@
 package websocket
 
 import (
+	"github.com/gorilla/websocket"
 	"log"
 	"time"
-	"github.com/gorilla/websocket"
 )
 
 const (
@@ -30,11 +30,21 @@ type InboundMessage struct {
 func (c *Client) ReadPump() {
 	defer func() {
 		c.Hub.Unregister <- c
-		c.Conn.Close()
+		if err := c.Conn.Close(); err != nil {
+			log.Printf("error closing connection in ReadPump: %v", err)
+		}
 	}()
 	c.Conn.SetReadLimit(maxMessageSize)
-	c.Conn.SetReadDeadline(time.Now().Add(pongWait))
-	c.Conn.SetPongHandler(func(string) error { c.Conn.SetReadDeadline(time.Now().Add(pongWait)); return nil })
+	if err := c.Conn.SetReadDeadline(time.Now().Add(pongWait)); err != nil {
+		log.Printf("error setting read deadline: %v", err)
+		return
+	}
+	c.Conn.SetPongHandler(func(string) error {
+		if err := c.Conn.SetReadDeadline(time.Now().Add(pongWait)); err != nil {
+			log.Printf("error setting read deadline in pong handler: %v", err)
+		}
+		return nil
+	})
 
 	for {
 		_, message, err := c.Conn.ReadMessage()
@@ -52,14 +62,21 @@ func (c *Client) WritePump() {
 	ticker := time.NewTicker(pingPeriod)
 	defer func() {
 		ticker.Stop()
-		c.Conn.Close()
+		if err := c.Conn.Close(); err != nil {
+			log.Printf("error closing connection: %v", err)
+		}
 	}()
 	for {
 		select {
 		case message, ok := <-c.Send:
-			c.Conn.SetWriteDeadline(time.Now().Add(writeWait))
+			if err := c.Conn.SetWriteDeadline(time.Now().Add(writeWait)); err != nil {
+				log.Printf("error setting write deadline: %v", err)
+				return
+			}
 			if !ok {
-				c.Conn.WriteMessage(websocket.CloseMessage, []byte{})
+				if err := c.Conn.WriteMessage(websocket.CloseMessage, []byte{}); err != nil {
+					log.Printf("error writing close message: %v", err)
+				}
 				return
 			}
 
@@ -67,13 +84,19 @@ func (c *Client) WritePump() {
 			if err != nil {
 				return
 			}
-			w.Write(message)
+			if _, err := w.Write(message); err != nil {
+				log.Printf("error writing message: %v", err)
+				return
+			}
 
 			if err := w.Close(); err != nil {
 				return
 			}
 		case <-ticker.C:
-			c.Conn.SetWriteDeadline(time.Now().Add(writeWait))
+			if err := c.Conn.SetWriteDeadline(time.Now().Add(writeWait)); err != nil {
+				log.Printf("error setting write deadline for ping: %v", err)
+				return
+			}
 			if err := c.Conn.WriteMessage(websocket.PingMessage, nil); err != nil {
 				return
 			}
diff --git a/server/src/internal/feature/quiz/websocket/hub.go b/server/src/internal/feature/quiz/websocket/hub.go
index f051320..f85a699 100644
--- a/server/src/internal/feature/quiz/websocket/hub.go
+++ b/server/src/internal/feature/quiz/websocket/hub.go
@@ -75,7 +75,6 @@ func (h *RoomHub) registerClient(client *Client) {
 	}()
 }
 
-
 func (h *RoomHub) unregisterClient(client *Client) {
 	h.mu.Lock()
 	defer h.mu.Unlock()
@@ -88,7 +87,7 @@ func (h *RoomHub) unregisterClient(client *Client) {
 		return
 	}
 
-	var isHost bool = false
+	isHost := false
 	if roomData != nil {
 		hostPlayer, hostPlayerExists := roomData.Players[roomData.HostID]
 		if hostPlayerExists && hostPlayer.Name == userID {
@@ -115,26 +114,26 @@ func (h *RoomHub) unregisterClient(client *Client) {
 				// DynamoDB から削除
 				if err := h.DBHandler.DeleteRoom(roomID); err != nil {
 					log.Printf("error: failed to delete room from DB: %v", err)
-				for otherClient := range room {
-					if otherClient != client { // 自分自身（ホスト）は除く
-						close(otherClient.Send) // 各クライアントのSendチャネルを閉じると、WritePumpが終了し接続が切れる
+					for otherClient := range room {
+						if otherClient != client { // 自分自身（ホスト）は除く
+							close(otherClient.Send) // 各クライアントのSendチャネルを閉じると、WritePumpが終了し接続が切れる
+						}
 					}
+					delete(h.rooms, roomID)
+				} else if len(h.rooms[roomID]) == 0 {
+					delete(h.rooms, roomID)
+					log.Printf("Room %s closed", roomID)
+				} else {
+					leaveMsg := &types.Message{
+						Type:    "user_left",
+						Payload: map[string]string{"userId": userID},
+						RoomID:  roomID,
+					}
+					go h.broadcastMessage(leaveMsg)
 				}
-				delete(h.rooms, roomID)
-			} else if len(h.rooms[roomID]) == 0 {
-				delete(h.rooms, roomID)
-				log.Printf("Room %s closed", roomID)
-			} else {
-				leaveMsg := &types.Message{
-					Type:    "user_left",
-					Payload: map[string]string{"userId": userID},
-					RoomID:  roomID,
-				}
-				go h.broadcastMessage(leaveMsg)
 			}
 		}
 	}
-	}
 }
 
 func (h *RoomHub) broadcastMessage(message *types.Message) {
diff --git a/server/src/internal/feature/room/repository/roomRepository.go b/server/src/internal/feature/room/repository/roomRepository.go
index 87f889b..aa27f84 100644
--- a/server/src/internal/feature/room/repository/roomRepository.go
+++ b/server/src/internal/feature/room/repository/roomRepository.go
@@ -1,4 +1,3 @@
-
 package repository
 
 import (
diff --git a/server/src/internal/feature/room/service/errors.go b/server/src/internal/feature/room/service/errors.go
index 9a8fce1..8c12d0b 100644
--- a/server/src/internal/feature/room/service/errors.go
+++ b/server/src/internal/feature/room/service/errors.go
@@ -3,6 +3,6 @@ package service
 import "errors"
 
 var (
-	ErrRoomNotFound       = errors.New("room not found")
-	ErrNotHostPermission  = errors.New("only the host can delete the room")
+	ErrRoomNotFound      = errors.New("room not found")
+	ErrNotHostPermission = errors.New("only the host can delete the room")
 )
diff --git a/server/src/internal/feature/room/types/roomType.go b/server/src/internal/feature/room/types/roomType.go
index 8e33090..bc0c69a 100644
--- a/server/src/internal/feature/room/types/roomType.go
+++ b/server/src/internal/feature/room/types/roomType.go
@@ -17,7 +17,6 @@ type Player struct {
 	IsReady bool   `json:"isReady" dynamodbav:"is_ready"`
 }
 
-
 // Room は個々のゲームルームの全情報
 type Room struct {
 	RoomID    string            `json:"roomId" dynamodbav:"room_id"`
@@ -28,7 +27,6 @@ type Room struct {
 	CreatedAt time.Time         `json:"createdAt" dynamodbav:"created_at"`
 }
 
-
 // --- リクエスト/レスポンス用の構造体 ---
 
 // RoomCreationRequest はルーム作成時のリクエストボディ
diff --git a/server/src/internal/feature/room/utils/errors.go b/server/src/internal/feature/room/utils/errors.go
index c5d9ff0..c6a4054 100644
--- a/server/src/internal/feature/room/utils/errors.go
+++ b/server/src/internal/feature/room/utils/errors.go
@@ -3,6 +3,6 @@ package utils
 import "errors"
 
 var (
-	ErrRoomNotFound       = errors.New("room not found")
-	ErrNotHostPermission  = errors.New("only the host can delete the room")
+	ErrRoomNotFound      = errors.New("room not found")
+	ErrNotHostPermission = errors.New("only the host can delete the room")
 )