1. A comparing device for comparing a reference image and a registered image, comprising: a hierarchical image generator generating a plurality of hierarchical images of different resolutions, with the raw image as a high-resolution image of the highest resolution, with this high-resolution image as the highest level; a registered image storage storing a plurality of registered images of the same resolution as the reference image; a registered image reader reading out, one-at-a-time, registered images stored in the registered image storage; a feature region setting device setting a feature region, determined in advance, for either a hierarchical image of the reference image, generated by the hierarchical image generator, or a hierarchical image of the reference image corresponding to a hierarchical image of the reference image of a registered image read out by the registered image reader; a corresponding region searching device searching, in the other hierarchical image, a corresponding region that corresponds to the feature region of the hierarchical image for which the feature region is set by the feature region setting device; and a first recorded image candidate selector selecting a registered image candidate for comparing a registered image, read out by the registered image reader, to a reference image based on a similarity between a feature region that is established for one hierarchical image by the feature region setting device and a corresponding region, found in the other hierarchical image, by a corresponding region finding device.