A biometric authentication device, comprising: a biometric information acquisition section configured to acquire input biometric information of a user, and generate input biometric data representing the input biometric information; a storage section configured to store therein registered biometric data representing registered biometric information about at least one registered user who is registered in advance; a first verification process section configured to execute a first verification process of calculating a first degree of similarity representing a degree of similarity between the input biometric information and the registered biometric information; a second verification process section configured to execute a second verification process of calculating a second degree of similarity representing the degree of similarity between the input biometric information and the registered biometric information by verifying the input biometric information against the registered biometric information with higher precision than with the first verification process by using a different algorithm than the first verification process; an authentication assessment section configured to authenticate, when the first or second degree of similarity takes a value larger than a predetermined verification assessment threshold value, the user as a registered user corresponding to the registered biometric information; a verification history update section configured to store the first degree of similarity calculated by the first verification process into the storage section in correlation with the registered biometric data representing the registered biometric information verified against the input biometric information; and a verification process change section configured to change, by referring to the first degree of similarity correlated with the registered biometric data stored in the storage section, when an authentication success rate indicating a rate of authenticating the registered user as the user is determined as showing an over-time reduction, the first verification process to the second verification process for execution to the registered biometric information. a biometric information acquisition section configured to acquire input biometric information of a user, and generate input biometric data representing the input biometric information; a storage section configured to store therein registered biometric data representing registered biometric information about at least one registered user who is registered in advance; a first verification process section configured to execute a first verification process of calculating a first degree of similarity representing a degree of similarity between the input biometric information and the registered biometric information; a second verification process section configured to execute a second verification process of calculating a second degree of similarity representing the degree of similarity between the input biometric information and the registered biometric information by verifying the input biometric information against the registered biometric information with higher precision than with the first verification process by using a different algorithm than the first verification process; an authentication assessment section configured to authenticate, when the first or second degree of similarity takes a value larger than a predetermined verification assessment threshold value, the user as a registered user corresponding to the registered biometric information; a verification history update section configured to store the first degree of similarity calculated by the first verification process into the storage section in correlation with the registered biometric data representing the registered biometric information verified against the input biometric information; and a verification process change section configured to change, by referring to the first degree of similarity correlated with the registered biometric data stored in the storage section, when an authentication success rate indicating a rate of authenticating the registered user as the user is determined as showing an over-time reduction, the first verification process to the second verification process for execution to the registered biometric information.