function newImage(arg) {
	if (document.images) {
		rslt = new Image();
		rslt.src = arg;
		return rslt;
	}
}

function changeImages() {
	if (document.images && (preloadFlag == true)) {
		for (var i=0; i<changeImages.arguments.length; i+=2) {
			document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
		}
	}
}

var preloadFlag = false;
function preloadImages() {
	if (document.images) {
		id01_first_o = newImage("image/01_preface_o.gif");
		id02_history_o = newImage("image/02_history_o.gif");
		id03_1st_hosai_o = newImage("image/03_1st_hosai_o.gif");
		id04_2nd_hosai_o = newImage("image/04_2nd_hosai_o.gif");
		id05_rokansai_o = newImage("image/05_rokansai_o.gif");
		id06_rokansai_o = newImage("image/06_rokansai_o.gif");
		id07_activity_o = newImage("image/07_activity_o.gif");
		id08_link_o = newImage("image/08_link_o.gif");
		id09_reference_o = newImage("image/09_reference_o.gif");
		id10_english_o = newImage("image/j_to_e_o.gif");
		preloadFlag = true;
	}
}