An authentication system includes a first controller that performs wireless communication with a mobile terminal and a first authentication unit that executes authentication of the mobile terminal including ID authentication and code authentication through the wireless communication performed between the first controller and the mobile terminal. The first authentication unit executes the code authentication by determining whether a terminal-side calculation result obtained by the mobile terminal matches a controller-side calculation result obtained by the first controller. The authentication system further includes a second controller that communicates with the mobile terminal and a second authentication unit that applies encryption communication using a portion of the terminal-side calculation result and a portion of the controller-side calculation result to communication performed between the second controller and the mobile terminal and authenticates the encryption communication.