There is provided user equipment of a radio communication system including the user equipment, a base station, and a core network apparatus including a reception unit configured to receive information indicating one or more types of NAS protocols supported by the core network apparatus from the base station; a selection unit configured to select a type of a NAS protocol to be transmitted to the core network apparatus based on the information indicating the one or more types of the NAS protocols received by the reception unit; and a transmission unit configured to transmit a NAS message of the type of the NAS protocol selected by the selection unit to the core network apparatus.