var pic= new Array('i1','i2','i3','i4','i5')
var num = 0;
var itv = 4000; //間隔、単位ミリセカンド ie. 4000=4sec
function showPic () {
document.images['img'].src = 'image/' + pic[num] + '.gif';
num++;
if(num > 4) num = 0;
setTimeout('showPic()', itv);
}