function timeImg() {
	var now = new Date();
	var Hour = now.getHours();
	var image, css;
	//時間で画像を差し替える
	if (Hour >= 19 || Hour < 6) {
		image = "images/main_visual03.jpg";
	} else if (Hour >= 16) {
		image = "images/main_visual02.jpg";
	} else {
		image = "images/main_visual01.jpg";
	}
	//スタイルシート書き出し
	css = "<style type=\"text/css\"><!--\n";
	css += "h1 span { background-image:url(" + image + "); }\n";
	css += "--></style>\n";
	document.write(css);
}
//実行
timeImg();