A CDMA system which can quickly establish initial synchronization of long codes which are spread-spectrum codes having periods which are much longer than the symbol length. The system inserts a priori codes which have a correlation value of nearly zero with respect to the long codes and an autocorrelation value which changes triangularly into spread-spectrum signals whose bandwidth is spread by the long codes at regular intervals, detects the timing at which reception of a priori codes is started, and estimates the reception phase of the long codes. The system is provided with an a priori code inserting circuit on the transmitting side and an a priori code replica generating circuit on the receiving side. The system is also provided with a plurality of correlators for finding the correlation value between the received signal and the replica of the a priori signal and a circuit for finding the maximum correlation value among the correlation values and its reception starting timing. The system estimates the timing at which that a priori signal is received from the reception starting timing at which the maximum correlation value is obtained, and infers that the point of time at a fixed time interval from the estimated timing is the point of phase reception of the long codes.