Some of a plurality of frame images are made comparison object images for use in synthesizing a still image. Selecting one of the comparison object images as a comparison reference image and one as a target image, the comparison reference image and target image are compared, and a parameter is calculated. If the parameter does not meet a predetermined criterion, the target image is excluded from the comparison object images. Additionally, any number of frame images from among the plurality of frame images are set as comparison object images, and the aforementioned comparison is carried out until the total number of comparison object images and reference images serving as reference for synthesis is equal to or greater than a predetermined number. A synthesized image generating module 75 synthesizes the reference images and comparison object images whose total number is equal to or greater than the predetermined number, to generate a still image.