A mobile IP data communication system is provided, which is capable of preventing dropouts of packet addressed to the mobile station at the time of switching the packet control station as a result of movement of the mobile station. A packet on an IP data connection that is used by the above-stated mobile station is forwarded to a next packet control station from a previous packet control station of the mobile station. The order of packets is correctly maintained by executing a process that a packet delivered to the next packet control station from the access router while the forwarding is in progress is buffered and a forwarding packet is put through ahead of such buffered packet or is forwarded only up to a time point when a packet from the access router is delivered.