The present invention provides a personal authentication apparatus that includes a permissibility information file for registering information indicating whether setting an ID common to more than one person is permitted or not. In the apparatus, only if setting of an ID common to more than one person is prohibited, an information registering section refers to the permissibility information file to check whether or not a first ID currently obtained for registration is identical to any of second IDs stored in an information storing section. Then, only if the first ID differs from any of the second IDs, the information registering section registers the first ID and biometric information currently obtained in an information storing section.