PURPOSE: To avoid an incapable state for transmission of the electric power, by giving the wave detection to the optical signal which is transmitted through an optical fiber and supplying the electric power necessary for an optical fiber communication device.

CONSTITUTION: An optical fiber cable 11 contains optical fiber lines 8 and 10. The optical signal transmitted through the line 10 is received by a receiving diode 12 such as a photodiode, etc. Thus the photoelectric converting current corresponding to the light receiving power can be extracted out of the diode 12. The detection output of the diode 12 is supplied to an optical repeater 7 after being stabilized by a voltage stabilizing circuit 13. The optical signal detected at the repeater 7 and through the line 8 is transmitted via an optical fiber 14.