if (document.images) { 

var img1on = new Image();
img1on.src = "img/plan/plan_20/bottun_on.gif"; 
var img1off = new Image();
img1off.src = "img/plan/plan_20/bottun_off.gif";
 
var img2on = new Image();
img2on.src = "img/plan/plan_20/pageup_on.gif"; 
var img2off = new Image();
img2off.src = "img/plan/plan_20/pageup_off.gif";

} 
// ポイント時の処理 
function On(name) { 

if (document.images) { 
document.images[name].src = eval(name + 'on.src'); 
} 

} 
// 放した時の処理 
function Off(name) { 

if (document.images) { 
document.images[name].src = eval(name + 'off.src'); 
} 

}