function smartRollover() {
	if(document.getElementsByTagName) {
		var images = document.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."));
		}
		images[i].onmouseout = function() {
		this.setAttribute("src", this.getAttribute("src").replace("_on.", "_off."));   
                }   
}
}
}
}
if(window.addEventListener) {
window.addEventListener("load", smartRollover, false); //実行
}
else if(window.attachEvent) {
window.attachEvent("onload", smartRollover);
}
else{
window.onload = smartOver;
}