<!--#mainImg内のimg要素に.activeをランダムで付加-->
$(window).load(function () {
	var len = $("#mainImg img").length;
	
	var rand = Math.floor( Math.random() * len);
	$("#mainImg img").eq(rand).attr("class","active");

	$("#mainImg img.active").fadeIn("slow");
	
	setInterval( "slideSwitch()", 4000 );
	setTimeout( "imgBlock()",4000);

});
function imgBlock() {
	$("#mainImg img").css('display', 'block');
}

function slideSwitch() {
	var $active = $('#mainImg img.active');
	//もしも$img01の中がカラだったら#mainImg内の最後のimg要素を入れる
	//if ( $img01.length == 0 ) $img01 = $('#mainImg img:last');
	 
	var $next =  $active.next().length ? $active.next() : $('#mainImg img:first');
	
	$active.addClass('last');

	$next.css({opacity: 0.0})
		.addClass('active')
		.animate({opacity: 1.0}, 500, function() {
			$active.removeClass('active last');
	});
}