An authentication system, wherein an RF tag stores a first facial feature point extracted from a captured image of a user's face. In an authentication device, a wireless communication unit wirelessly reads and writes information from and to the RF tag. A controller adjusts wireless communication conditions of the wireless communication unit, and estimates a position of the RF tag according to a distance to the RF tag. The controller adjusts imaging conditions of an imaging unit. A position of the user is detected according to an imaging resulting from the imaging unit. A second facial feature point is extracted from an image of the user's face captured by the imaging unit, and is collated with the first facial feature point read from the RF tag. Based on a collation result, authentication of the user is performed.