if (document.images){
  preload_image_object = new Image();
  image_url = new Array();
  image_url[0] = "/common/images/navi_home_on.gif";
  image_url[1] = "/common/images/navi_outline_on.gif";
  image_url[2] = "/common/images/navi_project_on.gif";
  image_url[3] = "/common/images/navi_publication_on.gif";
  image_url[4] = "/common/images/navi_member_on.gif";
  image_url[5] = "/common/images/navi_recruit_on.gif";
  image_url[6] = "/common/images/navi_contact_on.gif";

  var i = 0;
  for(i=0; i<=3; i++) 
   preload_image_object.src = image_url[i];
 }