To achieve seamless handover of a mobile station between base stations having different frequency bands.

When a frequency difference between an ANCH1 assigned from a base station 14-1 and an ANCH2 informed from a base station 14-2 in response to the start of handover to the base station 14-2 is larger than its own used frequency band, a mobile station 12 requests the reallocation of the ANCH1 to the base station 14-1 (S300). When the frequency difference between the ANCH1 and the ANCH2 becomes not larger than the used frequency band of the mobile station 12, the mobile station 12 shifts its own used frequency band from the used frequency band of the base station 14-1 to a frequency band including the ANCH1 and the ANCH2 (S310). After that, the mobile station 12 establishes a connection with the base station 14-2 via the ANCH2 (S312-S322), disconnects the connection with the base station 14-1 (S324), and further shifts its own used frequency band to the frequency band of the base station 14-2 (S326).