It is so arranged that margins will not be produced in an image compositing area. Specifically, a user sets an amount of parallax. A stereoscopic image is displayed in an image compositing area and the stereoscopic image is adjusted to as to take on the set amount of parallax. It is determined whether margins will be produced within the image compositing area owing to the adjustment of amount of parallax. If margins will be produced, the stereoscopic image is enlarged in size to such an extent that margins will not be produced.