function rollImage()
{
  // ロールオーバーするボタン画像のクラス名（の一部）
  var class_name = "roll";

  if(!document.getElementById) return;
  var arrOriginals = document.getElementsByTagName('img');
  var arrPreloads = new Array();
  for(var i=0; i<arrOriginals.length; i++)
  {
    if(arrOriginals[i].className.indexOf(class_name)==-1){ continue; }
    arrOriginals[i].orgsrc = arrOriginals[i].src;
    arrOriginals[i].num = i;
    arrPreloads[i] = new Image();
    arrPreloads[i].src = arrOriginals[i].src.replace(/(\/).([^\/]+)$/, '$1o$2');
    arrOriginals[i].onmouseover = function()
    {
      if(arrOriginals[this.num].onmouseover0) arrOriginals[this.num].onmouseover0();
      this.src = arrPreloads[this.num].src;
    }
    arrOriginals[i].onmouseout = function()
    {
      if(arrOriginals[this.num].onmouseout0) arrOriginals[this.num].onmouseout0();
      this.src = arrOriginals[this.num].orgsrc;
    }
  }
}
window.onload = rollImage;