A first switch device operating in a master mode, a second switch device operating in a backup mode, and third switch devices operating in a member mode in an initial state are provided. The first switch device operating in the master mode transmits a first control signal at every predetermined period to the second switch device operating in the backup mode. The second switch device operating in the backup mode makes a transition to the master mode when it does not receive for a predetermined period the first control signal from the first switch device operating in the master mode, and transmits an initializing signal to the third switch devices operating in the member mode. When having received the initializing signal, each of the third switch devices operating in the member mode constructs a management communication channel with the second switch device operating in the master mode.