A biometric authentication method is disclosed. Biometric information is acquired from a pair of portions at right and left of a body. Collation feature data are generated from the biometric information for right and left. Similarity feature data are generated for calculating a similarity between the biometric information for right and left. A similarity score between right and left is calculated by using the similarity feature data. The collation feature data for right and left and the similarity score are registered in a registration database. Collation scores for right and left are calculated by comparing the collation feature data in the registration database, and other collation feature data generated in an authentication. It is determined whether the authentication is successful, by using the collation scores, the similarity score in the registration database, and another similarity score generated in the authentication.