diff --git a/core/group_instant.go b/core/group_instant.go
index 4fb32ba..d538fad 100644
--- a/core/group_instant.go
+++ b/core/group_instant.go
@@ -185,6 +185,47 @@ func (gi *groupInstant) join(gd *instantDoc, mid primitive.ObjectID, character a
 	return nil
 }
 
+func (gi *groupInstant) UpdateInstantDocument(w http.ResponseWriter, r *http.Request) {
+	var data struct {
+		Gid    primitive.ObjectID
+		Doc    primitive.M
+		Result string
+	}
+	if err := gocommon.MakeDecoder(r).Decode(&data); err != nil {
+		logger.Println("UpdateInstantDocument failed. Decode returns err :", err)
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+
+	gd := partyDoc{
+		id: data.Gid,
+		rh: gi.rh,
+	}
+	if err := gi.rh.JSONMSetRel(gd.strid(), "$.", data.Doc); err != nil {
+		logger.Println("UpdateInstantDocument failed. JSONMSetRel returns err :", err)
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+
+	// 업데이트 알림
+	gi.sendUpstreamMessage(&wshandler.UpstreamMessage{
+		Target: "#" + gd.strid(),
+		Body:   data.Doc,
+		Tag:    []string{"GroupDocFragment"},
+	})
+
+	if data.Result == "after" {
+		raws, err := gi.rh.JSONGetDocuments(data.Gid.Hex(), "$")
+		if err != nil {
+			logger.Println("QueryInstantDocument failed. JSONGetDocuments returns err :", err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+
+		gocommon.MakeEncoder(w, r).Encode(raws[0])
+	}
+}
+
 func (gi *groupInstant) Join(w http.ResponseWriter, r *http.Request) {
 	var data struct {
 		Gid       primitive.ObjectID
@@ -273,7 +314,7 @@ func (gi *groupInstant) leave(gd *instantDoc, mid primitive.ObjectID) error {
 	// mid한테는 빈 GroupDocFull을 보낸다. 그러면 지워짐
 	gi.sendUpstreamMessage(&wshandler.UpstreamMessage{
 		Target: mid.Hex(),
-		Body:   bson.M{"_gid": gd.Gid},
+		Body:   bson.M{},
 		Tag:    []string{"GroupDocFull", gd.strid()},
 	})