1. A composite image generating apparatus comprising: a first storage unit configured to store a motion to be combined and first composite image data in such a manner that the motion and the first composite image data correspond to each other; an input unit configured to input a plurality of items of image data; a first determining unit configured to determine whether or not the movement of a part changing over a plurality of items of image data input by the input unit is almost the same as the motion stored in the first storage unit; and a first composite unit configured to read the first composite image data stored in the first storage unit so as to correspond to the motion and combine the first composite data with the image data having the changing part, if the first determining unit determines that the movement is almost the same as the motion.