A biometric authentication device comprising: a biometric information acquiring unit configured to generate a sequence of partial images, different partial images representing different portions of biometric information of a user; a storage unit configured to store data concerning registered biometric information of a registered user; a correlation value calculation unit configured to, when receiving one partial image of the sequence of partial images from the biometric information acquiring unit, calculate a correlation value between a portion of biometric information represented on the one partial image and the registered biometric information; a partial similarity update unit configured to, based on the correlation value for the one partial image, update a partial similarity representing the degree of similarity between the registered biometric information and portions of biometric information represented on at least one previous partial image; an authentication unit configured to, every time the partial similarity is updated, authenticate, if the updated partial similarity is equal to or higher than an authentication judging threshold, the user as the registered user; and an image loading unit configured to load the next partial image of the sequence of partial images from the biometric information acquiring unit if the updated partial similarity is lower than the authentication judging threshold, but not to load the next partial image of the sequence of partial images from the biometric information acquiring unit if the updated partial similarity is equal to or higher than the authentication judging threshold. a biometric information acquiring unit configured to generate a sequence of partial images, different partial images representing different portions of biometric information of a user; a storage unit configured to store data concerning registered biometric information of a registered user; a correlation value calculation unit configured to, when receiving one partial image of the sequence of partial images from the biometric information acquiring unit, calculate a correlation value between a portion of biometric information represented on the one partial image and the registered biometric information; a partial similarity update unit configured to, based on the correlation value for the one partial image, update a partial similarity representing the degree of similarity between the registered biometric information and portions of biometric information represented on at least one previous partial image; an authentication unit configured to, every time the partial similarity is updated, authenticate, if the updated partial similarity is equal to or higher than an authentication judging threshold, the user as the registered user; and an image loading unit configured to load the next partial image of the sequence of partial images from the biometric information acquiring unit if the updated partial similarity is lower than the authentication judging threshold, but not to load the next partial image of the sequence of partial images from the biometric information acquiring unit if the updated partial similarity is equal to or higher than the authentication judging threshold.