Provided is a terminal authentication system including a client terminal and a server device. The client terminal transmits first information based on secret information different for each client terminal and a client certificate including a hash value of the secret information which is derived from the secret information, to a server device. The server device receives the first information and the client certificate, derives a hash value from the secret information based on the first information using a unidirectional function, and authenticates the client terminal on the basis of the derived hash value and the hash value of the secret information which is included in the client certificate.