When a mobile terminal transmitting/receiving a packet using a plurality of IP address types performs a handover to an access network (single address type connection network) permitting transmission/reception of a packet using a single IP address only, an IP address not permitted is unfortunately discarded at an access network as a handover destination. Disclosed is a technique configured so that a mobile terminal (UE 1) detecting a handover to the single address type connection network establishes a temporary connection with a mobility management gateway (PGW 5) and thereafter acquires an address of an ePDG 8 located at a core network and informs the ePDG of a communication state before the handover via a PDN using the temporary connection. The ePDG informs the PGW of the communication state of the UE before the handover. Thereby, the communication state of the UE before the handover is achieved with the PGW via the ePDG and the PDN.