A mobile node (MN) 100 selects an AP 302 in a subnetwork 300 as the next AP to which it is wirelessly connected, while it is present within a cell 203 corresponding to a subnetwork 200 and wirelessly connected to an AP 202 in the subnetwork 200. The MN 100 transmits data indicating a request for BETH and the next AP to which it is wirelessly connected to an AR 201 via L3 level communication, while the MN 100 is present within the cell 203. The AR 201 implements establishment of a BET between an AR 301 in the subnetwork 300 and itself. As a result, the MN 100 can still use a care of address adapted to the subnetwork 200 even after it is wirelessly connected to the subnetwork 300.