window.onload = function() {
	var ul_node = getChildElementsByTagName(document.getElementById("head-navi"), "ul");
	var li_list = getChildElementsByTagName(ul_node[0], "li");
	for (var i = 0; i < li_list.length; i++) {
		li_list[i].onmouseover = function() {
			var sub_menu = getChildElementsByTagName(this, "div");
			if (sub_menu[0]) {
				sub_menu[0].style.display = "block";
			}
		}
		li_list[i].onmouseout = function() {
			var sub_menu = getChildElementsByTagName(this, "div");
			if (sub_menu[0]) {
				sub_menu[0].style.display = "none";
			}
		}
	}
}

function getChildElementsByTagName(element, tag_name) {
	var list = Array();
	for (var i = 0; i < element.childNodes.length; i++) {
		if (element.childNodes.item(i).tagName && element.childNodes.item(i).tagName.toLowerCase() == tag_name.toLowerCase()) {
			list[list.length] = element.childNodes.item(i);
		}
	}
	return list;
}