An input unit inputs respectively a plurality of partial images corresponding to a user to be authenticated. An extraction unit extracts feature points of a fingerprint respectively from the plurality of partial images inputted. A generation unit synthesizes the feature points extracted respectively from the plurality of partial images and then generates feature point information for authentication. An acquisition unit acquires reference feature point information. A rotation unit performs phase rotation on the generated authentication feature point information so that a directional component, namely, a phase component, contained in the generated authentication feature point information approaches that contained in the acquired reference feature point information. An authentication unit authenticates the authentication feature point information whose phase has been rotated, based on the reference feature point information.