Abstract: A plurality of mesh-connecting ports interconnect a plurality of bridges including an own bridge and other bridges as a mesh network. A packet transmitter/receiver reciprocally transmits and receives packets between the plurality of bridges through the mesh-connecting ports. A shortest path constructing unit constructs the shortest path between the bridges through the packet transmitter/receiver. An STP processing unit, with the shortest path constructed between the bridges by the shortest path constructing unit, executes STP processing for activating the spanning tree protocol (STP) to provide redundancy to the mesh network.