A radio base station notifies a maximum allowable transmission rate of uplink user data to a mobile station by using a common transmission rate control channel. The mobile station increases the transmission rate of uplink user data up to the maximum allowable transmission rate by a predetermined step. When a predetermined condition is satisfied, the mobile station requests the radio base station to transmit a dedicated transmission rate control channel, The mobile station determines the transmission rate of uplink user data based on the dedicated transmission rate control channel transmitted from the radio base station.