A biometric authentication apparatus includes a storage unit which stores first shape data representing a shape of biometric information of a registered user's hand with fingers at a first posture and second shape data representing a shape of biometric information of the hand with the fingers at a second posture; a posture specification unit which calculates an index representing a third posture of fingers of a user's hand in a biometric image; a biometric information extraction unit which generates third shape data representing a shape of biometric information of the user's hand in the biometric image; and a correction unit which obtains corrected shape data by correcting the first or the second shape data to cancel a shape difference of the biometric information due to a difference between the third posture and the first or the second posture based on the index for matching.