function display_image(){

var iValue,rNumber;
var img1="<img src=\"pic/mainimage-odyssey.jpg\" width=\"900\" height=\"350\" alt=\"オデッセイ\">";
var img2="<img src=\"pic/mainimage-life.jpg\" width=\"900\" height=\"350\" alt=\"ライフ\">";
var img3="<img src=\"pic/mainimage-accord.jpg\" width=\"900\" height=\"350\" alt=\"アコード\">";


iValue = Math.random() * 3;
    rNumber = Math.ceil(iValue);
    if(rNumber == 0){rNumber++};
    document.write(eval("img" + rNumber));
    }