The purpose of this invention is to propose a fingerprint authentication device for locking/unlocking capable of easily registering or erasing fingerprint data causing no lowering of security without using a key, a keyboard, or the like. This fingerprint authentication device is provided with a fingerprint sensor 18 with power on by opening a cover 16, at an outer lock part 11, and a registering/erasing circuit 34 having a switching part 39 for switching a control part 40 over to a registering mode when the fingerprint data of the finger 35 detected by the fingerprint sensor 18 is not registered in a storage part 41, and over to an erasing mode when the fingerprint data is registered. In the registering mode, the fingerprint data detected by the fingerprint sensor 18 is stored in the storage part 41, and the fingerprint data detected by the fingerprint sensor 18 is erased from the storage part 41 in the erasing mode.