When a portion of an image is displayed, a range of the image which is being displayed can be easily recognized. Namely, when enlarged image data which corresponds to an enlarged display range shown by hatching is extracted from image data and displayed on a display, a portion of the image which is represented by the enlarged image data is displayed on the entire display surface of the display. Original image data is processed such that a frame which represents the enlarged display range is synthesized with the image represented by the original image data, and resultant image data is displayed, as a navigation image, in an upper right corner of the display surface of the display.