A correlation detecting apparatus is capable of securely detecting a M sequence code forming a reference for timing even when a plurality of signals with different amplitudes are time division multiplexed includes matched filter (82) for detecting a predetermined code from a received signal, an average amplitude detector circuit (83) for detecting an average amplitude of the received signal, and a divider circuit (84) for normalizing an output of the matched filter (82) by an output of the average amplitude detector circuit 83 are provided. The output of the matched filter (82) normalized by the divider circuit (84) is compared with a threshold value for outputting a correlation detecting signal. When a received signal level is large, the output level of the matched filter (82) becomes large. However, in this case because the average amplitude of the received signal also becomes large, a divided value of the output level of the matched filter (82) by the output level of the average amplitude detector circuit (83) makes almost no change. In contrast to this, the output level of the matched filter when an M sequence is received remains nearly constant irrespective of an input signal level. Therefore, the received signal of M sequence can be detected without fail from the output of the comparator circuit (85).