PURPOSE: A network duplex device is provided to marinating the path about an active or standby during current communication even in the failure of the duplex device, thereby providing basic communication without disorder. CONSTITUTION: A line sensing unit(201) sense a state of master network line and a standby network line. According to the line state information of the line sensing unit, a switching control command unit(202) outputs a switching control command for a line switching. According to the switching control command of the switching control command unit, a mechanical relay(203) connects a client port with one port between a master port and a standby port. The mechanical relay switches the network line.
