In a procedure for a mobile station (UE) to perform handover from a cell under the control of a radio base station (NB) of an UTRAN scheme to a cell under the control of a radio base station (eNB) of an E-UTRA scheme, a switching center (MME) of the E-UTRA scheme receives, from and the radio base station (eNB) of the E-UTRA scheme, a handover request acknowledge message including a transparent container including a security algorithm of an AS used in a communication between the mobile station (UE) and the radio base station (eNB) of the E-UTRA scheme; and the switching center (MME) of the E-UTRA scheme transmits, to a switching center (SGSN) of the UTRA scheme, a NAS PDU including the transparent container, a security algorithm of a NAS and a security processing parameter of the NAS.