An optical switching device comprising: a fiber (100, 200) for transmitting at least one of an active signal and a standby signal, and a supervisory control signal; a failure detection unit; and a supervisory control unit (50, 51) for switching a transmission path of the active signal upon reception of information on a detected transmission failure from the failure detection unit, characterized in that: said fiber is a multicore fiber (100, 200) having a plurality of cores (110, 120, 130, 210, 220, 230); the optical switching device is adapted to transmit the supervisory control signal to the core (110, 210) surrounded by the cores (120, 130, 220, 230) to which at least one of the active signal and the standby signal is transmitted; the failure detection unit is adapted to detect occurrence of the transmission failure of the active signal based on a transmission condition of the active signal and information from the supervisory control signal; and upon detection of the occurrence of the transmission failure of the active signal by the failure detection unit, the supervisory control unit (50, 51) is adapted to switch the transmission path of the active signal to a standby signal transmission core (230, 130) different from the one (120, 220) to which the active signal is transmitted. a fiber (100, 200) for transmitting at least one of an active signal and a standby signal, and a supervisory control signal; a failure detection unit; and a supervisory control unit (50, 51) for switching a transmission path of the active signal upon reception of information on a detected transmission failure from the failure detection unit, characterized in that: said fiber is a multicore fiber (100, 200) having a plurality of cores (110, 120, 130, 210, 220, 230); the optical switching device is adapted to transmit the supervisory control signal to the core (110, 210) surrounded by the cores (120, 130, 220, 230) to which at least one of the active signal and the standby signal is transmitted; the failure detection unit is adapted to detect occurrence of the transmission failure of the active signal based on a transmission condition of the active signal and information from the supervisory control signal; and upon detection of the occurrence of the transmission failure of the active signal by the failure detection unit, the supervisory control unit (50, 51) is adapted to switch the transmission path of the active signal to a standby signal transmission core (230, 130) different from the one (120, 220) to which the active signal is transmitted. said fiber is a multicore fiber (100, 200) having a plurality of cores (110, 120, 130, 210, 220, 230); the optical switching device is adapted to transmit the supervisory control signal to the core (110, 210) surrounded by the cores (120, 130, 220, 230) to which at least one of the active signal and the standby signal is transmitted; the failure detection unit is adapted to detect occurrence of the transmission failure of the active signal based on a transmission condition of the active signal and information from the supervisory control signal; and upon detection of the occurrence of the transmission failure of the active signal by the failure detection unit, the supervisory control unit (50, 51) is adapted to switch the transmission path of the active signal to a standby signal transmission core (230, 130) different from the one (120, 220) to which the active signal is transmitted.