var imgMax  = 1; //セットする画像の枚数。
var imgRand = Math.floor(Math.random() * imgMax);

if(imgRand == 0)       document.write('<script type="text/javascript" src="/js/flaload_banner5.js"></script>');
<!--
/*else if(imgRand == 1)  document.write('<script type="text/javascript" src="/js/flaload_banner2.js"></script>');
else if(imgRand == 2)  document.write('<script type="text/javascript" src="/js/flaload_banner3.js"></script>');
else if(imgRand == 3)  document.write('<script type="text/javascript" src="/js/flaload_banner4.js"></script>');
else if(imgRand == 4)  document.write('<script type="text/javascript" src="/js/flaload_banner5.js"></script>');*/
//->