PURPOSE: To simplify the relay/changeover/priority transmission control of data and the managing function by switching an optical signal transmitted in an optical transceiver of a system transmitting data by means of light and identifying a received optical signal.

CONSTITUTION: The transceivers 20∼22, 24 are constituted so that an optical signal transmitted from them is changed over to identify the wavelength of the received optical signal. The optical transceivers 20∼22, 24 are coupled to a photocoupler 23 by optical fiber calbes 26∼29 so that the transmitted optical signal of the optical transceivers 20∼22, 24 is received by any device other than the optical transceivers 20∼22, 24. The switching control of the output wavelength of a driver and the identification of the input wavelength to a receiver are performed by the optical transceivers 20∼22, 24 and transmission controllers 17∼19, 25 connected to them.