// マウスオーバー処理
function setElementClassById(elem, value) {
	if(document.getElementById) {
		var obj = document.getElementById(elem);
		if(value == "contents_on") {
			del_class = "contents_off";
		}else{
			del_class = "contents_on";
		}
		if(obj) {
			Element.removeClassName(elem, del_class);
			var element =document.getElementById(elem); 
			obj.className = element.className + " " + value;
		}
	}
}