Access method, mobile station and base station for CDMA mobile communication system

In a CDMA mobile communication system, for realizing a multiple-access, a common reverse channel 10 is divided into an access channel 10A and a message channel 10B. When data (packet) to be transmitted occurs in any mobile station 1-4, mobile station having data to be transmitted transmits a transmission request signal including information, such as packet size or the like, by using the access channel 10A. In contrast, base station 30 transmits a transmission permission signal, which designates a transmission timing of data and a spreading code to be used as transmitting, on the basis of the state of utilization of message channel 10B and the state of occurrence of data. Mobile stations 1-4 transmits data in accordance with the spreading code and the transmission timing which are designated from base station 30.