A relay device includes a communication unit, a first conversion unit, a second conversion unit, and a controller. The communication unit communicates with a client device and a service providing device. The first conversion unit performs a first conversion process for performing conversion between a language interpretable by each client device and a language interpretable by the relay device. The second conversion unit performs a second conversion process for performing conversion between a language interpretable by each service providing device and the language interpretable by the relay device. The controller performs control so that data sent from the client device is subjected to the first conversion process and then the second conversion process before transmitted to the service providing device and data sent from the service providing device is subjected to the second conversion process and then the first conversion process before transmitted to the client device.