function RandomImage(){
img = new Array();

//以下イメージ名指定（img[0] = "http://www.onealjapan.com/yyyy/XXXXXXXX.jpg";）

img[0] = "http://www.onealjapan.com/top/main00.jpg";
img[1] = "http://www.onealjapan.com/top/main01.jpg";
img[2] = "http://www.onealjapan.com/top/main02.jpg";
img[3] = "http://www.onealjapan.com/top/main03.jpg";
img[4] = "http://www.onealjapan.com/top/main04.jpg";
img[5] = "http://www.onealjapan.com/top/main05.jpg";

//ランダムに切り替え

n = Math.floor(Math.random()*img.length);
document.getElementById("main_image").setAttribute("src",img[n]);
}