// メイン画像を切り替える。
function changeImage()
{
	if( _nowImg == 1 )
	{
		_nowImg = 2;
		$( "#main_image1" ).fadeIn( 2000 );
		$( "#main_image2" ).hide();
		$( "#main_image3" ).hide();
		$( "#main_image4" ).hide();
	}
	else if( _nowImg == 2 )
	{
		_nowImg = 3;
		$( "#main_image2" ).fadeIn( 2000 );
		$( "#main_image1" ).hide();
		$( "#main_image3" ).hide();
		$( "#main_image4" ).hide();
	}
	else if( _nowImg == 3 )
	{
		_nowImg = 4;
		$( "#main_image3" ).fadeIn( 2000 );
		$( "#main_image1" ).hide();
		$( "#main_image2" ).hide();
		$( "#main_image4" ).hide();
	}
	else if( _nowImg == 4 )
	{
		_nowImg = 1;
		$( "#main_image4" ).fadeIn( 2000 );
		$( "#main_image1" ).hide();
		$( "#main_image2" ).hide();
		$( "#main_image3" ).hide();
	}
}