function calendar(date_month)
{

    var cal_date;
    var data = "";

    cal_date = date_month;

    if (cal_date == '') {
        var sys_date = new Date();
        var today = "" + sys_date.getFullYear() + (sys_date.getMonth()+1) + (sys_date.getDate() < 10 ? "0"+sys_date.getDate() : sys_date.getDate());
        cal_date = today;
    }

    data = "cal_date=" + cal_date;
    url = "calendar.php";

    var myAjax = new Ajax.Request(
        url,
        {
            method: 'get',
            parameters: data,
            onComplete: calendar_result
        });
}

function calendar_result(xmlhttp)
{

    var result = eval("(" + xmlhttp.responseText + ")");

    if (result.sts != "0") {
        location.href = "/error.php";
    }
    else {
        document.getElementById('calendar').innerHTML = result.contents;
    }

}