Provided are a radio communication system and user device that enable smooth interworking in a radio resource control (RRC) layer in the case of implementing interworking between systems by LTE assisted 5G, 5G assisted LTE, or the like. The radio communication system includes an eNB 100 conforming to LTE and a 5G-BS 200 conforming to 5G. The eNB 100 includes an RRC function unit 110 that performs control based on LTE-RRC, which is an RRC protocol in LTE. The 5G-BS 200 includes an RRC function unit 210 that performs control based on 5G-RRC, which is the RRC protocol in 5G. The RRC function unit 210 has at least a function not specified in LTE-RRC.