The present invention discourages effective illegal use of compromised biometric information in biometric authentication and allows biometric authentication to be securely continued even when some biometric information is compromised. A user authentication system compares extracted user features with a previously registered combination of features and authenticates the user on the basis of the result of the comparison. If the authentication is successful, the previously registered combination is replaced with a new combination of features that are registered for use in the subsequent authentication of the authentication object.