To reduce a time required for an attach process or a location registration process and to alleviate traffic congestion in a W-CDMA mobile communications system. When an attach process or location registration process takes place on a UE with respect to both a circuit switched domain and a packet switched domain, messages about the attach process or the location registration process are transmitted from the UE to the circuit switched domain and the packet switched domain through an RRC (Radio Resource Control) connection established between the UE and a radio access network device (i.e., a RAN). This makes it possible to update location information for mobility management in both circuit switched domain and packet switched domain through the RRC connection.