A communication system includes a communication device and a relay apparatus that are connected to a network with an external service. The communication device includes a communication unit connected to a browser-installed device and a controller configured to transmit data location information to the browser installed device and output location of the communication device. The relay apparatus includes a communication unit and a controller configured to receive a request, transmit predetermined data based on the request, get the communication-device location information, instruct the browser-installed device to output the communication-device location information, receive authentication data, get the communication-device location information or the correspondence information output by the browser-installed device, and instruct the browser-installed device to transmit the authentication data to the communication device.