Abstract: An optical fiber communication system using group transmission which transmits PCM information by utilizing an optical fiber group composed of a plurality of optical fibers. The PCM information in a plurality of optical fibers is stored in a memory of the system's sending terminal, the stored information of each memory is read out by simultaneous clock pulses so as to send out the information to a transmission line which is composed of a plurality of said optical fibers. A repeater is provided in the transmission line having at least one of the following circuits, an AGC circuit, a light element control circuit, a power supply circuit and a supervisory circuit. The supervisory circuit is commonly provided for checking a plurality of signals which is transmitted by the above-mentioned optical fibers.