var imgArr = new Array();
var displayId = "img_disp";

//サムネイル画像Change
function changeDisplayImg(display_id, src_url)
{
	document.getElementById(display_id).src = src_url;
}

function preloadImg(src_url)
{
	//画像のプリロード
	var img = new Image();
	img.src = src_url;
	
	imgArr.push(src_url)
	
	img.onload = function() { void(false) };
}

var listener = function(event)
{
	var rndIndex = Math.floor(Math.random() * imgArr.length);
	changeDisplayImg(displayId, imgArr[rndIndex]);
}

if(window.attachEvent) {
window.attachEvent("onload", listener);
} else if(window.addEventListener) {
window.addEventListener("load", listener, true);
}