PURPOSE: To resolve the delay of control due to an increase of the processing time by providing a direct exchanging system of optical multiplex concurrent signals, converting individual transmission signals into optical inherent signals with an optical band-pass filter and a polarizing filter, and instantly performing bidirectional transmission.

CONSTITUTION: The output signal from the arithmetic processor CPU of an automatic control device CAP is inputted to an optical signal output substrate P1A to drive a light emitting unit DO, and the light from the light emitting unit DO passes a optical band-pass filter FC1 and a polarizing filter FG1A to generate the optical signal for controlling individual apparatuses in a station and the inter-station signal. The optical signal reaches relay link devices SA, SB of all stations, however Only the polarizing filter FG1A of the optical signal input substrate P1A' of the relay link device SA of the station A has the polarization passing characteristic for this signal light, thus this signal light is fed to only the optical signal input substrate P1A' to drive a light detection drive unit DI, and only a relay RYA11 is operated.