var Mac   = navigator.userAgent.indexOf("Mac") != -1   ? true : false;
function mdown(e) {
	if (navigator.appName == "Microsoft Internet Explorer") {
		if (event.button == 2 || (Mac && (event.ctrlKey || event.keyCode == 91))) {
			alert("右クリックは利用できません。");
			return(false);
		}
	} else if (navigator.appName == "Netscape") {
		if (e.which == 3 || e.modifiers == 2 || e.ctrlKey) {
			alert("右クリックは利用できません。");
			return false;
		}
	}
}


if (document.all) {
	document.onmousedown = mdown;
	document.onkeydown = mdown;
} else if (document.layers) {
	window.captureEvents(Event.MOUSEDOWN | Event.modifiers | Event.KEYDOWN);
	window.onmousedown = mdown;
	window.onkeydown = mdown;
} else if(navigator.userAgent.indexOf("Netscape6")!=-1){
	document.onmouseup = mdown; 
	document.onkeydown = mdown;
}