1. A biometric authentication device that authenticates a user using a biological feature of the user, the biometric authentication device comprising: an illumination unit configured to illuminate a target which represents the biological feature; an image sensor configured to obtain a first captured image by capturing the target illuminated by the illumination unit, and obtain a second captured image by capturing the target not illuminated by the illumination unit; an acquisition unit configured to acquire from a storage unit a mask which has a target area approximating a shape of the target in the first and second captured images obtained by the image sensor; and a detection unit configured to detect light other than illumination light illuminated by the illumination unit based on the mask acquired by the acquisition unit and at least one of the first and second images.