When an image is touched on a touch screen, the image is displayed as if a touched side of the image is pressed down and an opposite side of the touched side is lifted up. Priority levels of peripheral portions of the image are set in accordance with up and down of the image. Rendering priority between images to be overlapped is determined in accordance with a dominant-subordinate relationship between the priority levels of the peripheral portions of the respective images to be in contact. One of the images is displayed in an overlapped portion of the images based on the rendering priority.