An authentication device includes: a memory; and a processor coupled to the memory and configured to: when a registration request including authentication information to be used during authentication is received from a terminal device, generate registration information using the authentication information and key information and store the registration information in the memory, and when an authentication request including input information to be handled as the target of the authentication is received from the terminal device, generate a result of the authentication based on the input information, the registration information, and the key information, and transmit the result of the authentication to the terminal device.