Abstract: In a method of automatically changing a frequency in a CDMA mobile communication system where multiple frequencies are assigned to a base transceiver station, states of an RFC, ACC, and SIC are periodically checked thus parts of them where errors are detected are cut off, a frequency processed by the part having the error is detected and excluded from overhead data, and, when the frequency which is processed by the part having the error is a fundamental frequency, other part is made to take charge of the fundamental frequency. Reversely, parts which are restored from an error state to a normal state are turned "ON", and the restored part is made to process the fundamental frequency as was before and a part which currently processes the fundamental frequency is made to process its original frequency when the restored part is one for the fundamental frequency.