In a biometric authentication device that includes biometric-authentication-data generating means for generating biometric authentication data from biometric data of a user, and authentication means for performing authentication of the biometric authentication data on the basis of reference biometric data of the user, a matching ratio of the reference biometric data and updated and registered second reference biometric data is calculated, and the user is requested to re-register the reference biometric data and the second reference biometric data when the matching ratio is lower than a predetermined threshold value.