Biometric authentication device and biometric authentication method

A biometric authentication method comprising:

• authenticating a user when biometric information of the user matches biometric information of a registrant by comparing the biometric information of the user acquired by a biometric information acquisition device with the biometric information of the registrant represented in data stored in a storage device;
• determining whether or not to allow use of a predetermined function according to a temporal change of a measured value of a distance to the user measured by a distance measurement device after the user has been authenticated;
• and
• controlling enabling and disabling of the function device based on a determination result of allowing or not allowing the use of the predetermined function,
• wherein the determining whether or not to allow the use of the predetermined function determines to allow the use of the predetermined function when a trajectory of the temporal change of the measured value of the distance after the user has been authenticated reaches within an activation range without the trajectory deviating from a predetermined tolerable range, and
• wherein the predetermined tolerable range shifts to become closer to the activation range in response to an elapsed time from a time when the user has been authenticated.

An authentication device comprising:

• a function device which executes a predetermined function;
• an input device which acquires authentication information of a user;
• a distance measurement device which measures a distance to the user to output a measured value of the distance;
• a storage device which stores authentication information of a registrant;
• a processor configured to:
• authenticate the user when the acquired authentication information of the user matches the authentication information of the registrant;
• determine whether or not to allow use of the predetermined function according to a temporal change of the measured value of the distance after the user has been authenticated;
• and
• control enabling and disabling of the function module based on a determination result of allowing or not allowing the use of the predetermined function,
• wherein the determination result allowing or not allowing the use of the predetermined function determines to allow the use of the predetermined function when a trajectory of the temporal change of the measured value of the distance after the user has been authenticated reaches within an activation range without the trajectory deviating from a predetermined tolerable range, and
• wherein the predetermined tolerable range shifts to become closer to the activation range in response to an elapsed time from a time when the user has been authenticated.