A new technique is disclosed, by which a mobile terminal after executing handover between subnets can quickly perform packet transmission to outside immediately after the handover. According to this technique, after deciding the execution of handover, MN (mobile terminal) 10 requests an external transmission address (link local address of an access router belonging to a subnet or of a default router after the handover) relating to a subnet connected after the handover at the same time as the transmitting of RtSolPr message to PAR21 connected before the handover. PAR acquires the external transmission address in response to the request and transmits the external transmission address to MN together with a response by PrRtAdv message to MN. MN sets up the external transmission address as acquired before the handover to the packet to be transmitted after the handover.