An object is to perform a priority control that is more elaborate than that is performed by using a QCI. In a mobile communication system according to the present invention, a mobility management node MME notifies a radio base station eNB, in an “Initial Context Setup procedure” or an “E-RAB Setup Procedure”, following pieces of information in an associated form: an “E-RAB ID” of an E-RAB to be established between a gateway device S-GW and a mobile station UE; one QCI that is assigned to the E-RAB; and one FPI that is assigned to data flow transmitted on the E-RAB. A radio base station eNB establishes, in response to the notification, one S1 bearer corresponding to the E-RAB between the gateway device S-GW and the radio base station and one DRB corresponding to the E-RAB between the mobile station UE and the radio base station.