A living body sensor obtains a plurality of living body images along an authentication-target living body, and a shape sensor obtains shape information corresponding to each of the plurality of living body images. A processor determines a position of a part of the authentication-target living body captured in each of the plurality of living body images, according to the shape information corresponding to each of the plurality of living body images. The processor compares a biometric feature of each of the plurality of living body images and a registered biometric feature by using a determined position of the part of the authentication-target living body and performs authentication for the authentication-target living body according to a comparison result of comparing the biometric feature of each of the plurality of living body images and the registered biometric feature.