pass = '/image/';
img = new Array('header_benri2_ov.jpg','header_kariru_ov.jpg','header_kinko_ov.jpg','header_rate_ov.jpg','header_tameru_ov.jpg','header_unyou_ov.jpg');
preimg = new Array;
for(i=0; i<img.length; i++){
  preimg[i] = new Image();
  preimg[i].src = pass+img[i];
}

var type = 'jpg'; // image TYPE
var url = '/image/'; // image Pass
function ChgImg(name,flg){
  if(flg=="on"){document.images[name].src = url+name+'_on.'+type;
  }else if(flg=="ov"){document.images[name].src = url+name+'_ov.'+type;
  }else if(flg=="of"){document.images[name].src = url+name+'_of.'+type;
  }
}