A transmission rate control method for controlling a transmission rate of a channel to which the transmission rate control method is applied, include: notifying, at a radio network controller, at a timing of a call setup or the like, a primary allowable transmission rate of the channel to which the transmission rate control method is applied; starting, at a mobile station, after the call setup, transmission at a transmission rate below the primary allowable transmission rate, when data to be transmitted is generated; and controlling, at the mobile station, the transmission rate of the channel to which the transmission rate control method is applied, based on an Relative Grant Channel transmitted from a radio base station.