1. A fingerprint reading method in which a system comprising a sweep type fingerprint sensor to read a series of partial fingerprint images which represent a fingerprint from a sliding finger executes: an image acquisition process of acquiring a partial fingerprint image read by the sweep type fingerprint sensor; a position calculation process of finding position information of the partial fingerprint image when the partial fingerprint image has been acquired in the image acquisition process; an image division process of cutting out a unique unit image corresponding to an image region having a predetermined area from the partial fingerprint image on the basis of the position information when the position information has been found in the position calculation process; and a feature extraction process of extracting feature information of the unit image when the unit image has been cut out in the image division process.