function change_navi_bg(position,img_url){
	var bg_url = img_url + "img/menu_over.jpg";
	document.getElementById("menu_" + position).style.background = "url('"+ bg_url + "')";
}

function change_navi_bg_back(position,img_url){	
	var bg_url = img_url + "img/service_bg_2.jpg";
	document.getElementById("menu_" + position).style.background = "url('" +bg_url + "')";
}