こんな感じ。 <script type="text/javascript"> function tumblr_background(a){ tObj=a['posts'];document.body.style.backgroundImage='url('+ tObj[Math.floor(Math.random()*24+1)]['photo-url-1280'] +')';document.body.style.backgroundAttachment='fixed'; } </script> <script type="text/javascript" src="http://[ユーザID].tumblr.com/api/read/json?start=0&num=24&type=photo&callback=tumblr_background"></script>