var randomImg = new Array();
randomImg[0]='<img src="images/keyvisual_01.jpg" width="690" height="215" border="0" alt="" />';
randomImg[1]='<img src="images/keyvisual_02.jpg" width="690" height="215" border="0" alt="" />';
randomImg[2]='<img src="images/keyvisual_03.jpg" width="690" height="215" border="0" alt="" />';

var imgNum = Math.floor(Math.random() * randomImg.length);