An OADM device is provided with a variable optical attenuator 73 for attenuating a light signal into which a received light signal is demultiplexed by an optical demultiplexing functional unit 71, a modulating circuit 7 for piggybacking an ID number of a corresponding transmitting port onto the light signal by using the variable optical attenuator, an optical reception detector 84 for detecting the light level of a light signal received via a receiving port, a demodulating circuit 85 for extracting the ID number from the light level detected by the optical reception detector, an ID number management unit 91 for determining whether the ID number extracted by the demodulating circuit matches an ID number set thereby, and a notifying unit 9 for notifying a connection failure occurring in an optical patch cable 14 when the ID number management unit determines that there is a mismatch between the ID numbers.