An address table can be easily shared (synchronized) between two switching devices for which multi-chassis link aggregation is set. When a destination port of a frame received at a port P2 is a port P1, one of the two switching devices for which the multi-chassis link aggregation is set creates a bridging frame containing a transmission source address contained in the flame and an identifier of the port which has received, and transfers the bridging frame from a bridging port. When the other of the two switching devices receives the bridging frame, the other of the two switching devices detects the identifier of the port which has received and the transmission source address from the frame, and updates an address table of its own based on the identifier, the transmission source address, and a link table of its own.