An optical communication system has a master station (10) and a plurality of slave stations (20-1 to 20-n) connected thereto via an optical fiber network (1), which is provided with an optical splitter (30) and a relay unit (10000) which relays signals transmitted/received between the master station and the plurality of slave stations. The master station includes a first controller (1000) for performing ranging between the master station and the relay unit, and the relay unit includes a second controller (11000) for performing ranging between the relay unit and the plurality of slave stations. The master station determines, on the basis of the results of ranging performed by the first and second controllers as well as reports from the slave stations, timings for the slave stations to transmit signals to the master station, and receives signals multiplexed through the optical fiber network from the slave stations.