The transmission control unit of the device transmits sample data while changing the setting of output amplitude and emphasis of the transmitter within a prescribed range. The transmission processing unit of the device generates an eye diagram from the sample data received by the receiver, detects receivable phase-range data from the eye diagram, and transmits the same. The optimization processing unit of the device writes the phase-range data transmitted from the device into the table in correspondence to the output amplitude and emphasis of which the setting has been changed, determines optimum values of output amplitude and emphasis from the table obtained upon the completion of setting change within the prescribed range, and sets the same in the transmitter of the device. Then, the device, serving as the transmitting side, determines optimum values of output amplitude and emphasis of the transmitter and sets the same.