var imageBox = new Array();
imageBox[0] = "index_bg1.gif";
imageBox[1] = "index_bg2.gif";
imageBox[2] = "index_bg3.gif";
imageBox[3] = "index_bg4.gif";
imageBox[4] = "index_bg5.jpg";

function changeImg(){
	var e = Math.floor(Math.random() * imageBox.length);
	document.getElementById("getBody").style.backgroundImage = "url(common/img/index/" + imageBox[e] + ")";
}

window.onload = changeImg;