now = new Date();
Month = now.getMonth()+1;
ranimg = new Array();
ranimg[0]="image1.jpg";
ranimg[1]="image2.jpg";
ranimg[2]="image3.jpg";
ranimg[3]="image4.jpg";
ranimg[4]="image5.jpg";
ranimg[5]="image6.jpg";
xx = Math.floor(ranimg.length*Math.random());
ranimg = ranimg[Math.floor(xx)];
document.write ('<style type="text/css"><!--#header {background-image: url("http://www.t-junshin.ac.jp/jhs/blogimg/pic/'+ Month +'/'+ ranimg +'");}--></style>');