Disclosed is a technique for allowing a mobility service provider to allocate a home agent appropriate for each individual mobile node. According to the technique, an MN 10 notifies the domain name of an MSP 3 to an ASP 1, and in response to the notified domain name of the MSP, the ASP notifies the address of an HA allocation server 3a to the MN. The MN transmits, to the notified address of the HA allocation server, an HA allocation request message including the domain name of the ASP. The HA allocation server selects an HA based on previously held correspondences between HAs 3b, 3c and one or more ASPs, and notifies the selected HA to the MN.