In a communication system in which a relay apparatus, a terminal apparatus, and other apparatuses, which can communicate with an authentication apparatus, are coupled through a communication path, the relay apparatus, and the terminal apparatus have unique authentication information, respectively. The relay apparatus transmits its own authentication information and authentication information collected from the terminal apparatus to the authentication apparatus. The authentication apparatus determines whether the relay apparatus and the terminal apparatus are authentic apparatuses based on the received authentication information. The relay apparatus shuts down communication between itself and an apparatus determined to be unauthentic based on a result of the determination, and transmits communication control information to shut down communication with the apparatus determined to be unauthentic to the terminal apparatus. The terminal apparatus shuts down the communication between itself and the apparatus determined to be unauthentic based on the communication control information.