function setListener(observer, eventType, callFunc){
	if(observer.attachEvent){
		observer.attachEvent('on' + eventType, callFunc);
	}else if(observer.addEventListener){
		observer.addEventListener(eventType, callFunc, false);
	}else {
		alert("このブラウザではイベントリスナが使用できません");
		return false;
	}
}

function initOnLoad(){
	setListener($("category_what"), "mouseover", menu_what_visible);
	setListener($("category_what"), "mouseout", menu_what_hidden);
	setListener($("category_event"), "mouseover", menu_event_visible);
	setListener($("category_event"), "mouseout", menu_event_hidden);
	setListener($("category_bbs"), "mouseover", menu_bbs_visible);
	setListener($("category_bbs"), "mouseout", menu_bbs_hidden);
}

function menu_what_visible(){
	menu_visible($("menu_what"));
}

function menu_what_hidden(){
	menu_hidden($("menu_what"));
}

function menu_event_visible(){
	menu_visible($("menu_event"));
}

function menu_event_hidden(){
	menu_hidden($("menu_event"));
}

function menu_bbs_visible(){
	menu_visible($("menu_bbs"));
}

function menu_bbs_hidden(){
	menu_hidden($("menu_bbs"));
}

function menu_visible(observer){
	observer.style.visibility = 'visible';
}

function menu_hidden(observer){
	observer.style.visibility = 'hidden';
}

setListener(window, "load", initOnLoad);