In a writing device, a controller controls an authentication communication unit so as to transmit authentication data to a display device, prior to writing main data into the display device, in order to specify the display device into which the main data is to be written. After carrying out the authentication, the controller controls a main communication unit so as to transmit the main data stored in a memory to the display device into which the main data is to be written, by wireless communication. In the display device, a controller controls an authentication communication unit so as to receive the authentication data from the writing device. The controller controls a main communication unit so as to receive the main data from the writing device by wireless communication after the completion of the authentication. Therefore, when the main data is written into the display device from the writing device, it is possible to avoid wiring problems, and provide the display device with an improved appearance.