diff --git a/backend/state-manager/pkg/connect/connect_handler.go b/backend/state-manager/pkg/connect/connect_handler.go
index 7fa85b41..ad6e1f55 100644
--- a/backend/state-manager/pkg/connect/connect_handler.go
+++ b/backend/state-manager/pkg/connect/connect_handler.go
@@ -120,6 +120,7 @@ func (s *StateManagerServer) UpdateStopState(
 			connect.CodeUnknown,
 			errors.New("db error"),
 		)
+		slog.Default().Error("db connection error", err)
 		return nil, err
 	}
 	mqtt_handler.NotifyStateUpdate("stop", req.Msg.State.Id, req.Msg.State.State.String())
diff --git a/backend/state-manager/pkg/db/db.go b/backend/state-manager/pkg/db/db.go
index 5736ee75..03995226 100644
--- a/backend/state-manager/pkg/db/db.go
+++ b/backend/state-manager/pkg/db/db.go
@@ -7,6 +7,7 @@ package db
 import (
 	"context"
 	"log"
+	"log/slog"
 	"os"
 
 	statev1 "github.com/ueckoken/plarail2023/backend/spec/state/v1"
@@ -21,24 +22,29 @@ var client *mongo.Client
 
 func Open() {
 	var err error
-	//log.Println("Connecting to MongoDB...")
+	slog.Default().Debug("Connecting to MongoDB...")
 	uri := os.Getenv("MONGODB_URI")
 	if uri == "" {
 		log.Fatal("No MONGODB_URI set")
 	}
+	// TODO: Open関数がctxを受けるようにして、そのctxの子contextをDBのコネクションに使う
 	client, err = mongo.Connect(context.TODO(), options.Client().ApplyURI(uri))
 	if err != nil {
+		// TODO: return err, do not panic!
+		slog.Default().Error("database connection failed", slog.Any("err", err))
 		panic(err)
 	}
-	//log.Println("Connected to DB!")
+	slog.Default().Debug("connected to DB")
 }
 
 func C() {
-	//log.Println("Closing connection to DB...")
+	slog.Default().Debug("Closing connection to DB...")
+	// TODO: contextを受けて、その子contextをDBクライアントに渡す
 	if err := client.Disconnect(context.TODO()); err != nil {
+		slog.Default().Error("DB Connection Closing failed")
 		log.Println(err)
 	}
-	//log.Println("Connection closed!")
+	slog.Default().Debug("DB Connection is successfully closed")
 }
 
 /*
@@ -81,6 +87,7 @@ func GetPoints() []*statev1.PointAndState {
 	collection := client.Database("state-manager").Collection("points")
 	cursor, err := collection.Find(context.Background(), bson.M{})
 	if err != nil {
+		slog.Default().Warn("Get Points failed", slog.Any("err", err))
 		panic(err)
 	}
 	var result []*statev1.PointAndState
diff --git a/go.mod b/go.mod
index 82f01763..fff44c56 100644
--- a/go.mod
+++ b/go.mod
@@ -9,7 +9,6 @@ require (
 	github.com/go-chi/httplog/v2 v2.0.7
 	github.com/joho/godotenv v1.5.1
 	go.mongodb.org/mongo-driver v1.13.0
-	golang.org/x/exp v0.0.0-20231108232855-2478ac86f678
 	golang.org/x/net v0.18.0
 	golang.org/x/sync v0.5.0
 	google.golang.org/protobuf v1.31.0
@@ -52,6 +51,7 @@ require (
 	golang.org/x/term v0.14.0 // indirect
 	golang.org/x/text v0.14.0 // indirect
 	golang.org/x/time v0.3.0 // indirect
+	golang.org/x/tools v0.15.0 // indirect
 	google.golang.org/appengine v1.6.7 // indirect
 	gopkg.in/inf.v0 v0.9.1 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
diff --git a/go.sum b/go.sum
index f7108caa..d9151842 100644
--- a/go.sum
+++ b/go.sum
@@ -113,8 +113,6 @@ golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5y
 golang.org/x/crypto v0.0.0-20220622213112-05595931fe9d/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/crypto v0.15.0 h1:frVn1TEaCEaZcn3Tmd7Y2b5KKPaZ+I32Q2OA3kYp5TA=
 golang.org/x/crypto v0.15.0/go.mod h1:4ChreQoLWfG3xLDer1WdlH5NdlQ3+mwnQq1YTKY+72g=
-golang.org/x/exp v0.0.0-20231108232855-2478ac86f678 h1:mchzmB1XO2pMaKFRqk/+MV3mgGG96aqaPXaMifQU47w=
-golang.org/x/exp v0.0.0-20231108232855-2478ac86f678/go.mod h1:zk2irFbV9DP96SEBUUAy67IdHUaZuSnrz1n472HUCLE=
 golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=