An authentication system includes: a reading unit that (i) reads ID information as a response to a first read command being a command to which only a first type of contactless communication terminal responds, and outputs the ID information and type information indicating that a contactless communication terminal is of the first type, and (ii) reads ID information as a response to a second read command being a command to which both the first and second types of contactless communication terminals respond, and causes additional issuance of the first read command, and when succeeding in reading ID information as a response to the additionally issued first read command, outputs the ID information and type information indicating the first type; an authentication unit that, when a user list includes an output pair of ID information and type information of the communicating contactless communication terminal, authenticates a user associated with output pair.