var img = new Array();
img[0] = '<img src="http://www.sibf.jp/images/mv/mv01_250.jpg" alt="Saga International Balloon Fiesta" />';
img[1] = '<img src="http://www.sibf.jp/images/mv/mv02_250.jpg" alt="Saga International Balloon Fiesta" />';
img[2] = '<img src="http://www.sibf.jp/images/mv/mv03_250.jpg" alt="Saga International Balloon Fiesta" />';
img[3] = '<img src="http://www.sibf.jp/images/mv/mv04_250.jpg" alt="Saga International Balloon Fiesta" />';


var no = Math.floor(Math.random() * img.length);
document.write(img[no]);