function randomAdv() {
// ランダム広告
  m = 0, x = 0, y = 0;
  ad  = new Array();
  adv = new Array();
  hit = new Array();

  // hitには相対確率を入れる
  // 完全にランダムにするなら全部"1"にする
  hit[0] = 1;  adv[0] = '<body bgcolor="#FFFFFF"><object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,0,0" height="300" width="948"><param name="movie" value="swf/top2.swf"><param name="quality" value="best"><param name="play" value="true"><embed height="300" pluginspage="http://www.macromedia.com/go/getflashplayer" src="swf/top2.swf" type="application/x-shockwave-flash" width="948" quality="best" play="true" wmode="transparent"><param name="wmode" value="transparent"></object></body>';
  hit[1] = 1;  adv[1] = '<body bgcolor="#FFFFFF"><object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,0,0" height="300" width="948"><param name="movie" value="swf/top.swf"><param name="quality" value="best"><param name="play" value="true"><embed height="300" pluginspage="http://www.macromedia.com/go/getflashplayer" src="swf/top.swf" type="application/x-shockwave-flash" width="948" quality="best" play="true" wmode="transparent"><param name="wmode" value="transparent"></object></body>';

  for(i=0; i<=hit.length - 1; i++) {
    m += hit[i]
  }
  n = Math.floor(Math.random() * m);
  n++;
  for(i=0; i<=hit.length - 1; i++) {
    x = y;
    y += hit[i];
    if(x<n && n<=y) ad = adv[i];
  }
  document.write(ad);
}

