A relay device employs a control system which notifies control data indicating its own specification to transmitting equipment to receive data in a form matching to its own specification and acquires control data D13 from receiving equipment employing the control system and connected to a latter stage. The relay device determines whether its own specification is in a higher order or not in comparison a specification indicated by the control data D13 with its own specification, and if it is determined that its own specification is in the higher order, rewrites the control data D13 from the receiving equipment by its own control data D12 to notify it to the transmitting equipment. Thereby, the relay device can reproduce the data from the transmitting equipment in accordance with its own specification. At this time, since the relay device converts the received data from the transmitting equipment to transmit it, even the receiving equipment can reproduce it in accordance with an appropriate specification.