In an image reproduction window, an image reproduction area in which images are reproduced, and an operating area in which a slide bar is displayed are provided. When a slider of the slide bar is moved, the number of images to be displayed in one frame in the image reproduction area is increased or decreased in accordance with a position of the slider. The number of images in one frame increases as a displacement amount of the slider increases. When the slider is moved within a range in which the number of images to be displayed in one frame does not change, only a frame change interval is changed while the number of images in one frame is unchanged.