A biometric authentication device including: a biometric information acquiring unit which generates a plurality of partial images, each of the partial images capturing a portion of biometric information of a user different from each other; a correlation value calculation unit which calculates the correlation value between a portion of biometric information represented on one partial image and registered biometric information; a partial similarity update unit which, based on the correlation value for the one partial image and the correlation value for at least one other partial image acquired before the one partial image, updates partial similarity representing the degree of similarity between the registered biometric information and portions of biometric information represented on the one partial image and the at least one other partial image; an authentication unit which authenticates, when the partial similarity is equal to or higher than an authentication judging threshold, the user as the registered user.