A transmission control method for uplink user data in a mobile communication system in which a plurality of HARQ processes is applied to the uplink user data, includes: classifying, at the radio network controller, each HARQ process into any of a scheduled transmission process, a non-scheduled transmission process, or a scheduled and non-scheduled transmission process in which either of the scheduled transmission or the non-scheduled transmission is performed; notifying, at the radio network controller, the classification result to the mobile station; and transmitting, at the mobile station, the uplink user data in each HARQ process to the radio base station using the scheduled transmission or the non-scheduled transmission, based on the notified classification result.