PURPOSE: To transmit and receive a light signal forth and back between a central controller and terminal equipment through one optical fiber by branching a trunk transmission line made of an optical fiber into a branch transmission line through the 1st branching device, and providing the 2nd branching device which branches the branch transmission line into a transmission line for transmission and a transmission line for reception in each terminal equipment.

CONSTITUTION: Light incident from a side A is outputted to sides B and C and light incident from the side B or C is outputted to only the side A, so that no light is transmitted between the sides B and C. Further, a transmission part 24 and a reception part 25 may be coupled directly with the sides B and C of the branching device 10 without using the transmission line 8 for transmission nor transmission line 9 for reception. A power line 26 uses a light emitting diode having good light emission efficiency to increase the level of the transmitted light signal and also uses a photodiode having good photoelectric conversion efficiency to increase the photodetection output, and consequently electric power is supplied from the central controller 1 to the terminal equipment 2 through the optical fiber 3, thereby eliminating the need for a power line 26.