How to custom data text value in autocomplete ?

How to custom data text value in autocomplete ?

Hello guys.
I have try show data and get value using autocomplete jquery. Textbox will show data choose and label will get value .But it's error

  1.  Uncaught TypeError: Cannot read property 'DEPARTMENT_ID' of undefined .
 This is data JSON when i see console.log
  1. Object {d: "[{"DEPARTMENT_ID":"D00000000001","DEPARTMENT_NAME"…"2015-05-05T00:00:00","EDIT_BY":"","FLAG":false}]"}
  2. d: "[{"DEPARTMENT_ID":"D00000000001","DEPARTMENT_NAME":"HR","DEPARTMENT_DES":"HR","EDIT_DATE":"2015-05-05T00:00:00","EDIT_BY":"","FLAG":false},
  3. {"DEPARTMENT_ID":"D00000000002","DEPARTMENT_NAME":"ACCOUNT","DEPARTMENT_DES":"ACCOUNT","EDIT_DATE":"2015-05-05T00:00:00","EDIT_BY":"","FLAG":false}]"
  4. __proto__: Object
and this is function
  1. function load_text() {
                $.ajax(
                {
                    type: "POST",
                    url: "../BUS/WebService.asmx/LIST_DEPARTMENT",
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    success: function (data) {
                        var valuetextbox = [];
                        $.each($.parseJSON(data.d), function (idx, obj) {
                            valuetextbox.push(obj.DEPARTMENT_NAME);
                        });
                        $('#txt_textbox').autocomplete({
                            source: valuetextbox,
                            select: function (event, ui) {
                                $("#label_value").val(ui.item.obj.DEPARTMENT_ID);
                            }
                        });
                    },
                    error: function (data) {
                        alert("Error load");
                    }
                });
            }