To prevent consecutive transmission of a relative transmission rate control channel (RGCH) including a "Down" command and minimize deterioration in the service quality due to "Down" commands from non-serving cells, a transmission rate control method controls, at a mobile station, a transmission rate of uplink user data by using a first relative transmission rate control channel received from a serving cell and a second relative transmission rate control channel received from a non-serving cell. In the transmission rate control method, a maximum frequency of transmitting the second relative transmission rate control channel which includes a down command for instructing to decrease the transmission rate of the uplink user data is a value fixed in a mobile communication system or a value notified by a radio network controller.