A spread spectrum communication system for performing spread spectrum communication by superimposing a pseudo noise signal on a transmitted signal. The system comprises traffic detecting means for detecting the traffic of the transmitted signal, and means for changing the clock frequency of the pseudo noise signal in accordance with the output from the traffic detecting means. The system may alternatively comprise transmission quality determining means for determining the transmission quality of the received signal, and means for changing the clock frequency of the pseudo noise signal in accordance with the transmission quality determined by the transmission quality determining means. In operation, the system offers improved S/N ratios where traffic is high or transmission quality is low, saves power where traffic is low or transmission quality is high, and ensures large margins of power control precision for mobile stations near the upper limit of the system's line capacity.