A monitor and control device includes a monitor and control unit transmitting to a monitor target device a monitor and control signal (M&CS) through a M&CS path in a case of a malfunction occurred in a main signal path, and transmits to the monitor target device the M&CS through the main signal path in a case of a malfunction occurred in the M&CS path, the monitor target device including: a first path connection unit connected to the main signal path passing either a main signal in which the M&CS for monitoring and controlling the monitor target device is multiplexed or a main signal in which the M&CS is not multiplexed; a second path connection unit connected to the M&CS path passing the M&CS; and a selection unit selecting whether to perform transmission and reception of the M&CS by either one of the main signal path and the M&CS path.