How to get data value of object JSON string?

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jQuery

JSON

webservice

I have a JSON string , I want to get value of JSON string property.I try

$.ajax({
    type: "POST",
    url: "../BUS/WebService.asmx/GET_TRANSACTION_NEW",
    data: JSON.stringify(DTO),
    contentType: "application/json; charset=utf-8",
    dataType: 'json',
    success: function (data) {
        //console.log(data);
        var obj = $.parseJSON(data.d);
        alert(obj.DEPARTMENT_NAME);
    },
    error: function (data) {
        alert("Error");
    }
});

But it's not work , it's show alert

undefined

. This is console log data

Object {d: "[{"DEPARTMENT_ID":"D00000000001","DEPARTMENT_NAME"…"2015-05-05T00:00:00","EDIT_BY":"","FLAG":false}]"}
d: "[{"DEPARTMENT_ID":"D00000000001","DEPARTMENT_NAME":"HR","DEPARTMENT_DES":"HR","EDIT_DATE":"2015-05-05T00:00:00","EDIT_BY":"","FLAG":false},{"DEPARTMENT_ID":"D00000000002","DEPARTMENT_NAME":"ACCOUNT","DEPARTMENT_DES":"ACCOUNT","EDIT_DATE":"2015-05-05T00:00:00","EDIT_BY":"","FLAG":false}]"
__proto__: Object

Give me some advices, thank you