The present invention provides a technique to prevent the generation of a large number of binding update messages in an overlay network when a mobile node changes connection points. According to this technique, in a communication system where a home agent HA 1210 for holding BCE (Binding Cache Entry) of a mobile node MN 1220 and a plurality of proxy home agents pHA 1212, pHA 1214 and pHA 1216 each capable to operate as a proxy of HA 1210 are overlaid on a global communication network 1200, and BCE of MN 1220 held by HA 1210 is delegated to pHA 1214 where MN 1220 is connected. Further, when MN 1220 is re-connected to pHA 1216 of move destination different from pHA 114 of move source, BCE of MN 1220 delegated to pHA 1214 of move source is re-delegated to pHA 1216 of move destination.