If a trouble, which occurred in a node managing positional information, has been solved, the positional information can be restored only by transmitting a position registration request addressed to one multicast address without need to transmit multiple position registration requests addressed to multiple mobile terminals (MN). There are included a home agent, a mobile anchor point and a communication node, each of which is a node connected to a network. Each node receives a position registration from a mobile terminal, copies a binding cache to produce a backup binding cache, and maintains and manages the backup binding cache. When recovering from a trouble, each of the home agent, mobile anchor point and communication node searches for the backup binding cache to acquire the binding cache held before occurrence of the trouble; then designates an already registered multicast address for a mobile terminal stored in the acquired binding cache; sends a packet of position registration request to the mobile terminal; regards the acquired binding cache as being valid when a response to the position registration request packet is received from the mobile terminal; and then continues to maintain and manage the acquired binding cache.