Abstract: The optical communication system of the invention comprises an optical transmission line, optical coupling devices, each having a varying coupling ratio, connected to the transmission line, and stations connected to the optical coupling devices; wherein the coupling ratio of the device is changed to a predetermined value by a control signal applied by its associated station, depending on the state of transmission and reception, level of received signal, operating state of the station, and the like, to thereby provide high reliability, reduced transmission delay and low error rate, as well as to thereby decrease the amount of attenuation between transmitting and receiving stations.