A biometric authentication apparatus comprising: a storage unit arranged to store representative matching data that represent features of biometric information of a registered user and that represent conditions of a designated body part of the registered user, each representing one of at least two different portions of a variation range over which the condition of the body part containing the registered user's biometric information varies due to cyclic environmental variations; a biometric information acquiring unit arranged to generate a biometric image that represents biometric information of a user; a matching data generating unit arranged to generate, from the biometric image, input matching data that represents the features of the biometric information of the user; a matching unit arranged to match the input matching data against at least one of the representative matching data and compute a first matching score that indicates the degree of similarity between first matching data representing a given condition of the registered user's body part and the input matching data; an authentication judging unit arranged to judge, based on a result of the matching, whether the user is to be authenticated as being the registered user or not; and a representative matching data updating unit arranged to obtain a minimum value of the first matching score by examining temporal variation of the first matching score computed each time the user is authenticated as being the registered user, and to take the input matching data corresponding to the minimum value as being one of the representative matching data of the at least two different portions. a storage unit arranged to store representative matching data that represent features of biometric information of a registered user and that represent conditions of a designated body part of the registered user, each representing one of at least two different portions of a variation range over which the condition of the body part containing the registered user's biometric information varies due to cyclic environmental variations; a biometric information acquiring unit arranged to generate a biometric image that represents biometric information of a user; a matching data generating unit arranged to generate, from the biometric image, input matching data that represents the features of the biometric information of the user; a matching unit arranged to match the input matching data against at least one of the representative matching data and compute a first matching score that indicates the degree of similarity between first matching data representing a given condition of the registered user's body part and the input matching data; an authentication judging unit arranged to judge, based on a result of the matching, whether the user is to be authenticated as being the registered user or not; and a representative matching data updating unit arranged to obtain a minimum value of the first matching score by examining temporal variation of the first matching score computed each time the user is authenticated as being the registered user, and to take the input matching data corresponding to the minimum value as being one of the representative matching data of the at least two different portions.