function menu() {

	var url = location.href;
	var navi = document.getElementById('menu').getElementsByTagName('a');

	for(var i=0; i < navi.length; i++) {
		if(navi[i] == url){
			var elem = $('btn'+[i+1]);
			elem.className = 'btn'+[i+1]+'_on';
		}	
	}
	
}

/*
if(window.addEventListener) {
	window.addEventListener("load", menu, false);
}
else if(window.attachEvent) {
	window.attachEvent("onload", menu);
}
*/