In node devices composing a ring network connected to another network with a redundant node device, a topology table includes redundancy information of the redundant node device, a transmitter transmits topology information and the redundancy information of the node devices themselves, a topology table preparing portion prepares a topology table based on redundancy information and topology information received from the redundant node device, and topology information received from the other node device, and a packet distributor distributes a packet received over the ring network based on the topology table.