var img1_on=new Image();
	var img1_off=new Image();
	var img2_on=new Image();
	var img2_off=new Image();
	var img3_on=new Image();
	var img3_off=new Image();
	var img4_on=new Image();
	var img4_off=new Image();
	
	img1_on.src="imgs/header_1b.jpg";
	img1_off.src="imgs/header_1a.jpg";
	img2_on.src="imgs/header_2b.jpg";
	img2_off.src="imgs/header_2a.jpg";
	img3_on.src="imgs/header_3b.jpg";
	img3_off.src="imgs/header_3a.jpg";
	img4_on.src="imgs/header_4b.jpg";
	img4_off.src="imgs/header_4a.jpg";


// マウスオーバー処理
	function rollon(targetimage) {
		if(targetimage=="image1"){
	    	document.images[targetimage].src=img1_on.src;
	    }
	    if(targetimage=="image2"){
	    	document.images[targetimage].src=img2_on.src;
	    }
	    if(targetimage=="image3"){
	    	document.images[targetimage].src=img3_on.src;
	    }
	    if(targetimage=="image4"){
	    	document.images[targetimage].src=img4_on.src;
	    }
	}

	// マウスアウト処理
	function rolloff(targetimage) {
		if(targetimage=="image1"){
	    	document.images[targetimage].src=img1_off.src;
	    }
	    if(targetimage=="image2"){
	    	document.images[targetimage].src=img2_off.src;
	    }
	    if(targetimage=="image3"){
	    	document.images[targetimage].src=img3_off.src;
	    }
	    if(targetimage=="image4"){
	    	document.images[targetimage].src=img4_off.src;
	    }
	}