In authentication based on an image region in which the surface of a target object has been read, authentication is carried out on the basis of the location to which the image region corresponds. An authentication server (2) receives an image region to be authenticated, in which the surface of a target object possessed by a user has been read, together with an authentication request for said user, and from a plurality of pre-stored reference image regions, in which the surfaces of each of a plurality of target objects have been read, identifies one reference image region corresponding to the image region to be authenticated, and identifies the location to which said image region to be authenticated corresponds, and then carries out the authentication in response to the authentication request on the basis of the identified location.