window.onload =  function() {
    bgs = new Array();
    bgs[0] = "http://blog69.fc2.com/a/afunishi/file/theme_h1_takedajo.png";
    bgs[1] = "http://blog69.fc2.com/a/afunishi/file/theme_h1_hasagi.png";
    bgs[2] = "http://blog69.fc2.com/a/afunishi/file/theme_h1_utashinai.png";
    bgs[3] = "http://blog69.fc2.com/a/afunishi/file/theme_h1_rokko.png";
    bgs[4] = "http://blog69.fc2.com/a/afunishi/file/theme_h1_inari.png";
    bgs[5] = "http://blog69.fc2.com/a/afunishi/file/theme_h1_santome.png";
    bgs[6] = "http://blog69.fc2.com/a/afunishi/file/theme_h1_tonda.png";
    randomNumber = Math.round(Math.random() * (bgs.length - 1));
    bgProperty = 'url("'+ bgs[randomNumber] +'")';
    document.getElementById("header").style.backgroundImage = bgProperty;
}