Abstract: An HA function can be stopped and restarted without having an influence on MN performing registration and other nodes. The HA function is transferred and controlled by procedures established by an IP address managing procedure for operating plural IP addresses and stopping this operation, an IP address transfer control request procedure for transferring and controlling the IP address and an IP address transfer control response procedure (A12, A17), a tunneling procedure for establishing a bidirectional tunnel and transmitting and receiving a packet formed as a capsule, an IPsec transfer control request procedure for transferring and controlling an IPsec function and an IPsec transfer control response procedure (A13, A18), a registration transfer control request procedure for transferring and controlling registration by HA with respect to another HA and a registration transfer control response procedure (A14, A19).