A transmitting circuit transmits data to which an error detection code is attached to a receiving circuit via a transmission path. When detecting the error of the data received via the transmission path, a receiving circuit transmits a retransmit request for the data in which the error is detected to the transmitting circuit. The receiving circuit enters a termination unit adjustment period using the error detection of the received data as a trigger and updates the resistance values of a receiving side termination unit installed at the termination of the transmission path to an appropriate value within the termination unit adjustment period.