A packet ring network system including a plurality of packet ring networks to which nodes are brought into ring form connection so that a packet inside a ring obtained by encapsulating a client packet, which a terminal outside the packet ring network transmits, is transmitted and received in a packet ring network. A plurality of subpacket ring networks are connected to the first packet ring network through an interlink used for client packet transport therebetween. The interlink is provided to each of the subpacket ring networks connected to the first packet ring network. The first packet ring network and each of the subpacket ring networks include an interlink node connected to an interlink.