function addRule( selector, property ) {
	if( document.styleSheets[0].addRule ) //IE
		document.styleSheets[0].addRule( selector, "{" + property + "}" );
	else if( document.styleSheets[0].insertRule ) //Mozilla
		document.styleSheets[0].insertRule( selector + "{" + property + "}", document.styleSheets[0].cssRules.length );
	else
		return false;
}

function AlertStyle(){
	if(navigator.userAgent.indexOf("MSIE") != -1){ // 文字列に「MSIE」が含まれている場合
		addRule("div.error","display:none");
		addRule(".caution","background:#fdc");
	}else{
		var alert_css = document.getElementById('alert_css');
		var textNode = document.createTextNode('<!-- .caution {background:#fdc;} .error {display:none;} //-->');
		alert_css.appendChild(textNode);
	}
}