n = Math.floor(Math.random()*12);
var strCSS = '<style type="text/css">';
strCSS += '#banner { ';
strCSS += 'background-image: url(http://mejirushi.com/mt/banner/0' + n + '.jpg); ';
strCSS += 'background-repeat:no-repeat; ';
strCSS += 'width : 650px; ';
strCSS += 'height : 231px; ';

strCSS += '}';
strCSS += '</style>';
document.write(strCSS);