A technique is disclosed to decrease unnecessary routing during communication between a mobile node and a correspondent node in case a home agent of the mobile node is a mobile home agent. According to this technique, HA 112 positioned in a home network 102 and HA 114 of MN 130 are included. In a communication system, where HA 114 is a mobile home agent, and a mobile network 104 of HA 114 is hierarchized under the home network 102, HA 114, which is a home agent, discovers HA 112 positioned in the home network 102 when it is detected that it is away from the home network 102 and delegates binding cache entry of MN 130 under its own management to HA 112 so that HA 112 acts as a home agent for MN 130.