function smartOver() {
	smartRollover('mainmenu');
	smartRollover('contents');	
}
function smartRollover(idName) {
	if(document.getElementsByTagName) {
		var images = document.getElementById(idName).getElementsByTagName("img");
		for(var i=0; i < images.length; i++) {

	if(images[i].getAttribute("src").match(/_off\./)) {
	fileName = new Array(images[i].getAttribute("src").replace("_off.", "_on."));
	preImages = new Array();
	for (j=0; j<fileName.length; j++) {
		preImages[j] = new Image();
		preImages[j].src = fileName[j];	 //「_on」の画像をプリロード
}

		images[i].onmouseover = function() {
		this.setAttribute("src", this.getAttribute("src").replace("_off.", "_on."));	//マウスオーバーで_off→_on
}
		images[i].onmouseout = function() {
			this.setAttribute("src", this.getAttribute("src").replace("_on.", "_off."));	//マウスが離れたら_on→_off
			}
		}
		}
	
	}
}
if(window.addEventListener) {
window.addEventListener("load", smartOver, false);	//実行
}
else if(window.attachEvent) {
window.attachEvent("onload", smartOver);
}
else{
window.onload = smartOver;
}