The utility model discloses an optical fiber monitoring device comprising a photoelectric converter connected to an output terminal of an optical fiber in an optical cable of an optical fiber communication system and converting received optical signals into electric signals; a transmission line configured to transmit the electric signals to an alarm circuit at a predetermined distance from the photoelectric converter; and the alarm circuit. An input terminal of the alarm circuit is connected to the transmission line and outputs alarm signals when no electric signal from the photoelectric converter is received via the transmission line. The alarm circuit comprises a resistor, of which one end is an input terminal of the alarm circuit and the other end is connected to an anode of an LED, a relay which at least comprises two input terminals and two output terminals and the LED which connected between the two input terminals of the relay. The two output terminals output alarm signals. The optical fiber monitoring device of the utility model can monitor optical fiber faults at a long distance in real time and can simply obtain fault alarm signals.