An image processing section 10 calculates degree of similarity among a plurality of image frames of dynamic image data, determines scene-change frames based on the calculated degree of similarity, and performs automatic editing and preparation of a digest dynamic image of the dynamic image data by merging a specified duration of frames, giving priority to scenes whose scene-change frame has a low degree of similarity to an immediately preceding frame or some preceding frames, or by merging, from scenes delimited by a scene change, a specified duration of frames having a degree of similarity in keeping with the user's indication of whether or not a “little change digest” or a “much change digest” is to be prepared.