A transmission rate control method includes: measuring, at a radio base station, a reception power of a DPCH transmitted from the mobile station; extracting, at the radio base station, a transmission data block size of the uplink user data from an E-DPCCH; acquiring, at the radio base station, a transmission power ratio of an E-DPDCH to the DPCCH which corresponds to the extracted transmission data block size; calculating, at the radio base station, a reception power of the E-DPDCH based on the measured reception power and the acquired transmission power ratio; calculating, at the radio base station, a relative transmission rate of the uplink user data based on the calculated reception power; notifying, at the radio base station, the relative transmission rate to the mobile station via a E-RGCH; and controlling, at the mobile station, the transmission rate based on the notified relative transmission rate.