Each of MCLAG devices has a MCLAG table, a port control unit, and a relay processing unit. The MCLAG table retains one or a plurality of first ports in association with a first identifier. The port control unit controls a first port group to transmission/reception permitted state when the first port group is set to active, and controls the first port group to a transmission prohibited state when the first port group is set to standby. The relay processing unit relays a frame containing the first identifier as a destination port to the first port group when the first port group is controlled to the transmission/reception permitted state, and relays the same to a bridge port when the first port group is controlled to the transmission prohibited state.