An imaging device is configured to include an imaging lens, an imaging unit which acquires image data based on an optical image of a subject received via the imaging lens, a motion detector which detects a motion of the subject based on image data sequentially obtained from the imaging unit, a focus detector which calculates focus position data based on the image data obtained from the imaging lens when the motion detector detects a motion of the subject, and an in-focus position estimating unit which estimates an in-focus position based on the calculated focus position data.