var img1_on=new Image();
var img2_on=new Image();
var img3_on=new Image();
var img4_on=new Image();
var img5_on=new Image();
var img1_off=new Image();
var img2_off=new Image();
var img3_off=new Image();
var img4_off=new Image();
var img5_off=new Image();

img1_on.src="parts/ico_home_b.png";
img1_off.src="parts/ico_home_a.png";
img2_on.src="parts/ico_story_b.png";
img2_off.src="parts/ico_story_a.png";
img3_on.src="parts/ico_chara_b.png";
img3_off.src="parts/ico_chara_a.png";
img4_on.src="parts/ico_event_b.png";
img4_off.src="parts/ico_event_a.png";
img5_on.src="parts/ico_down_b.png";
img5_off.src="parts/ico_down_a.png";

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;
	}
	if(targetimage=="image5") {
		document.images[targetimage].src=img5_on.src;
	}
}

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;
	}
	if(targetimage=="image5") {
		document.images[targetimage].src=img5_off.src;
	}
}