A code division multiple access (CDMA) mobile communication system with improvements to permit stable reception with a minimum of bit error. The system includes a base station and a mobile station for communicating with the base station. The mobile station includes an oscillator, a radio frequency demodulator for demodulating a radio frequency band signal received from the base station by use of a first signal from the oscillator, a radio frequency modulator for modulating a second signal to be transmitted by use of the first signal from the oscillator, and an antenna for receiving the radio frequency band signal transmitted from the base station, and for transmitting the modulated second signal to the base station. An oscillation frequency of the oscillator is controlled by use of a change of phase shift detected using the demodulated radio frequency band signal received from the base station.