var theLength    = 4;
var randomNumber = Math.floor(Math.random() * theLength) + 1;
function changeBg(){
	document.write('<style type="text/css">');
	document.write('<!--');
	document.write('.bgImgTop01 { background-image:url(images/top/top_img0' +randomNumber+ '_01.jpg);}');
	document.write('.bgImgTop02 { background-image:url(images/top/top_img0' +randomNumber+ '_02.jpg);}');
	document.write('.bgImgTop03 { background-image:url(images/top/top_img0' +randomNumber+ '_03.jpg);}');
	document.write('//-->');
	document.write('</style>');

}