A transmission rate control method for controlling a transmission rate of uplink user data to be transmitted by a mobile station, based on a maximum allowable transmission rate, include: instructing, at a radio network controller, to change a serving cell of the mobile station, to the mobile station; and controlling, at the mobile station, the maximum allowable transmission rate without following an increase command of the maximum allowable transmission rate which is notified from a current serving cell to which the mobile station is connected, between a timing when the mobile station receives the instruction from the radio network controller and a timing when a change process of changing the serving cell of the mobile station is completed.