//* 画像自動切換

var n = 0;
var imgDB   = new Array("/images/img_mainback.jpg","/images/img_mainback_sub_b.jpg","/images/img_mainback_sub.jpg");
var timeDB  = new Array(10000,10000,10000);
var layName ='mainBG';

function changeBG(){
  if (n<3){
    setTimeout("changeBG()",timeDB[n]);
    if(document.layers) { //Netscape用
      document.layers[layName].background.src = imgDB[n] ;
    } else {
      if(document.all){ //IE用
         document.all(layName).style.backgroundImage = 'url('+imgDB[n]+')';
      }
    }
    n++;
  }
  else{
    clearTimeout();
    n = 0;
    changeBG();
  }
}