window.onload = function(){ 

var imgobj01 = new Image(900,180);
var imgobj02 = new Image(900,180);
var imgobj03 = new Image(900,180);
var imgobj04 = new Image(900,180);
var imgobj05 = new Image(900,180);
var imgobj06 = new Image(900,180);

imgobj01.src = "http://www.shachihoko-ch.com/img/header2.png";
imgobj02.src = "http://www.shachihoko-ch.com/img/header3.png";
imgobj03.src = "http://www.shachihoko-ch.com/img/header4.png";
imgobj04.src = "http://www.shachihoko-ch.com/img/header5.png";
imgobj05.src = "http://www.shachihoko-ch.com/img/header6.png";
imgobj06.src = "http://www.shachihoko-ch.com/img/header7.png";


var imgs = new Array();
imgs[0]=imgobj01;
imgs[1]=imgobj02;
imgs[2]=imgobj03;
imgs[3]=imgobj04;
imgs[4]=imgobj05;
imgs[5]=imgobj06;


var n = Math.floor(imgs.length*Math.random());
var img = imgs[Math.floor(n)];
var imgobj = document.getElementById('topheader');
imgobj.src = img.src;


}