1. A moving body detecting device comprising: a motion information acquirer that acquires motion information on an imaging device capable of performing imaging with a first exposure time and a second exposure time longer than the first exposure time; an approximate image generator that generates an approximate image generated by approximating one of a first photographic image imaged with the first exposure time and a second photographic image imaged with the second exposure time to another photographic image, on the basis of the motion information; and a moving body detector that detects a moving body captured in the first and second photographic images, on the basis of the approximate image and the another photographic image.