To provide a user authentication method and device capable of lowering both probability that a person registered by combining a password with living body recognition cannot be authenticated and probability that a person not registered is authenticated.

This user authentication method for authenticating a user by a password inputted from the outside and living body recognition information of the user such as a fingerprint, an iris and a face characteristically includes steps for: (a) determining whether the password is inputted or not; (b) setting a first threshold obtained by lowering FRR of a threshold used in a living body recognition part when the password is inputted and coincides with a registered one, and for setting a second threshold obtained by lowering FAR when the password does not coincide with the registered one; and (c) determining whether or not the user is authenticated by comparing the living body recognition information of the user inputted from the outside with registered living body recognition information, and proceeding to the step (a) when the user is not authenticated. Thereby, the password is organically connected to the living body recognition part and the password input result affects the performance of the living body recognition part, or the living body recognition result is fed back to affect the next authentication process to improve both FAR and FRR.