An authentication system that executes user authentication processing in accordance with an authentication request includes at least one first device. The first device has a biological information acquiring unit that is configured to acquire biological information of a user, and a first authentication unit that outputs an authentication result of which the user is authenticated, based on the biological information. The authentication system includes a second device that is configured to communicate with the first device. The second device has an information acquiring-storing unit that is able to store identification information of the first device beforehand, a determination unit that is configured to determine whether the first device is registered, and a second authentication unit that is configured to perform user authentication, in accordance with an authentication result output by the first authentication unit, when the determination unit determines that the first device is registered.