function initRollOvers() { 
    if (!document.getElementById){ 
        return; 
    } 
        var preLoads = new Array(); 
    var allImages = document.getElementsByTagName('img'); 
  
    for (var i = 0; i < allImages.length; i++) {                if (allImages[i].className == 'btn') { 
            var src = allImages[i].getAttribute('src'); 
            var ftype = src.substring(src.lastIndexOf('.'), src.length); 
            var oSrc = src.replace(ftype, '_in'+ftype); 
  
            //-- スワップ元、スワップ先画像の登録 
            allImages[i].setAttribute('pSrc', src); 
            allImages[i].setAttribute('oSrc', oSrc); 
  
            //-- イメージのプリロード 
            preLoads[i] = new Image(); 
            preLoads[i].src = oSrc; 
  
            //-- イベントの設定 
            allImages[i].onmouseover = function() { 
                this.setAttribute('src', this.getAttribute('oSrc')); 
            } 
            allImages[i].onmouseout = function() { 
                this.setAttribute('src', this.getAttribute('pSrc')); 
            } 
        } 
    } 
} 
  
function addOnload(func){ 
    if ( typeof window.addEventListener != "undefined" ){ 
        window.addEventListener( "load", func, false ); 
    }else if ( typeof window.attachEvent != "undefined" ) { 
        window.attachEvent( "onload", func ); 
    }else{ 
        if ( window.onload != null ){ 
            var oldOnload = window.onload; 
            window.onload = function ( e ) { 
            oldOnload( e ); 
            window[func](); 
        }; 
    }else 
        window.onload = func; 
    } 
} 
addOnload(initRollOvers);