diff --git a/sgip/receiver.go b/sgip/receiver.go
index 3e77ce8..0e9e893 100644
--- a/sgip/receiver.go
+++ b/sgip/receiver.go
@@ -79,7 +79,7 @@ func (r *Receiver) worker(id int) {
 
 		log.Println("worker ", id, ": Accept ", conn)
 
-		session := NewSession(conn, r.handler, r.done)
+		session := NewSession(conn, r.handler, r.done, r.debug)
 		// block
 		session.Run()
 	}
diff --git a/sgip/session.go b/sgip/session.go
index e419e41..f71fcd1 100644
--- a/sgip/session.go
+++ b/sgip/session.go
@@ -20,9 +20,15 @@ type Session struct {
 	isClose    uint64
 	done       chan struct{}
 	serverDone chan struct{}
+
+	// debug flag
+	debug bool
 }
 
-func NewSession(connection net.Conn, handler Handler, done chan struct{}) *Session {
+func NewSession(
+	connection net.Conn, handler Handler,
+	done chan struct{}, debug bool,
+) *Session {
 
 	return &Session{
 		handler:    handler,
@@ -30,6 +36,7 @@ func NewSession(connection net.Conn, handler Handler, done chan struct{}) *Sessi
 		pipe:       make(chan protocol.Operation),
 		done:       make(chan struct{}),
 		serverDone: done,
+		debug:      debug,
 	}
 }
 
@@ -102,6 +109,10 @@ func (s *Session) recvWorker() {
 			return
 		}
 
+		if s.debug {
+			log.Println(op)
+		}
+
 		s.pipe <- op
 	}
 }