img = new Array();
img[0] = "./images/mailmaga_kokuchi1.gif";
img[1] = "./images/mailmaga_kokuchi2.gif";
img[2] = "./images/mailmaga_kokuchi3.gif";
img[3] = "./images/mailmaga_kokuchi4.gif";
n = Math.floor(Math.random()*img.length);
document.write("<img src='"+img[n]+"' border='0'>");