bg = new Array();
bg[0] = "img/topimage1.jpg";/変えたい背景画像URL/
bg[1] = "img/topimage2.jpg";/ ↑ /
bg[2] = "img/topimage3.jpg";/ ↑ /
bg[3] = "img/topimage4.jpg";/ ↑ /
bg[4] = "img/topimage5.jpg";/ ↑ /
bg[5] = "img/topimage6.jpg";/ ↑ /
bg[6] = "img/topimage7.jpg";/ ↑ /
bg[7] = "img/topimage8.jpg";/ ↑ /
bg[8] = "img/topimage9.jpg";/ ↑ /
bg[9] = "img/topimage10.jpg";/ ↑ /
bg[10] = "img/topimage11.jpg";/ ↑ /
back_g = Math.floor(bg.length * Math.random());
document.write("<img src='"+bg[back_g]+"' width='800px' height='240px' alt='秋田の写真～WE LOVE AKITA' /> ");