The present invention relates to a transmission rate control method for controlling a transmission rate of user data transmitted from a mobile station to a radio base station, including: notifying, from a radio network controller to the radio base station, a transmission rate difference or a transmission rate ratio between a transmission rate of a mobile station performing a soft handover and a transmission rate of a mobile station not performing the soft handover, the soft handover performed between the mobile station and the radio base station under the radio network controller; and controlling, at the radio base station, the transmission rate of each mobile station according to the notified transmission rate difference or the notified transmission rate ratio.