PURPOSE: To ensure an automatic elimination of the multipath distortion of the FM broadcast which has no special reference signal, by installing the memory to store the self-correlation signal and the means to inspect the nature of the self-correlation signal.

CONSTITUTION: Correlation waveform memory 8 plus comparing circuits 5 and 6 are provided. The received signal is supplied to correlation unit 1 through signal converting circuit 9, and the input signal S(t) is sampled in the section of NT. And the sample value Si (i=0∼N) is stored in input waveform memory 2. On the other hand, correlation arithmetic circuit 3 calculates successively sample value K (K= 0∼N) of correlation signal (t) in section NT and based on the data of Si. Then value RW of K at the time when the values of O and K become O/2 are compared with threshold levels A and B set previously each at circuits 5 and 6. And when the conditions of O≥A and RW<B are detected, the waveform near O is regarded as the impulse. And based on data K at that moment, the contents of memory 8 is rewritten.