A transmission rate control method of this invention includes: notifying, at a radio base station Node B, a mobile station UE of a maximum allowable transmission rate of uplink user data, using an absolute rate grant channel (E-AGCH); instructing, at a radio network controller RNC, the mobile station UE to reduce the maximum allowable transmission rate by layer-3 signaling; and reducing, at the mobile station UE, the maximum allowable transmission rate according to the instruction from the radio network controller RNC, and controlling, at the mobile station UE, a transmission rate of the uplink user data based on the reduced maximum allowable transmission rate.