1. A biometric authentication device that authenticates a user using a biological feature of the user, the biometric authentication device comprising: an illumination device configured to emit light toward 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 device, and obtain a second captured image by capturing the target not illuminated by the illumination device; a processor configured to acquire from a storage 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 to detect light other than the light emitted by the illumination device based on the acquired mask and at least one of the first and second images.