var iValue, rNumber;

var img1 = new Image();
var img2 = new Image();
var img3 = new Image();
var img4 = new Image();
var img5 = new Image();
var img6 = new Image();
var img7 = new Image();
img1 = "http://www.dynac50.jp/img/change/west/0.jpg";
img2 = "http://www.dynac50.jp/img/change/west/1.jpg";
img3 = "http://www.dynac50.jp/img/change/west/2.jpg";
img4 = "http://www.dynac50.jp/img/change/west/3.jpg";
img5 = "http://www.dynac50.jp/img/change/west/4.jpg";
img6 = "http://www.dynac50.jp/img/change/west/5.jpg";
img7 = "http://www.dynac50.jp/img/change/west/6.jpg";

function display_image(){
iValue = Math.random() * 7;
rNumber = Math.ceil(iValue);
if(rNumber==0) rNumber++;
document.image1.src=eval("img" + rNumber);
}