For eliminating a reduction in throughput in a network as a whole according to optimum path transfer technique which is the expansion of spanning tree protocol, a frame switching unit of the network has an STP control unit for, when a port state of a spanning tree is changed, notifying a table control unit of an identifier of the spanning tree and a port number of a predetermined port among the respective ports, the table control unit for setting, in a forwarding table storage unit, a received port number of a predetermined port as an output port in an entry in which a node ID is equivalent to a spanning tree identifier, and a table search unit for determining an output destination from among output ports obtained by acquisition of received frame information from a frame analysis unit.