1. A moving amount detector that sets a movable member included in a device of amounting destination or an object conveyed by the device as a detection target and detects a moving amount of the detection target, the moving amount detector comprising: an imaging unit that repeatedly captures images of the detection target at a constant sampling period while the detection target moves; and a moving amount calculating unit that selects two images to be compared with each other among a series of images of the detection target captured by the imaging unit such that an imaging time difference between the two images is increased as a difference due to moving of the detection target is further generated between the two images and calculates a moving amount of the detection target based on the difference.