In a mobile communication network, the foreign agent function of a mobile terminal that makes a small number of moves is placed in a radio base station, and the foreign agent function of a mobile terminal that makes a large number of moves is placed in a first node setting and managing a radio access link with a mobile terminal connected through a radio base station, thereby preventing concentration of foreign agent functions on the first node. When a mobile terminal (MN) detects a move to a foreign link to be connected, it acquires a new c/o address and transmits a binding update request to which a communication party list is attached to a home agent. The home agent transmits a binding update request to report a pair of the new c/o address and the home address of the mobile terminal to the communication parties in the communication party list.