To automatically obtain optimal noise suppression and S/N improvement according to an input signal level by varying the response characteristics of an adaptive filter based on the input signal or on S/N of the adaptive filter.

A function for switching an adaptive following-up speed and the delay time of a delay circuit according to the received signal of a receiver is added to an adaptive filter 1. An input signal y(n) is inputted to the adaptive filter 1, and this input signal y(n) is inputted to a delay circuit 3. A difference (error) signal between the output of the adaptive filter 1 and the output of the delay circuit 3 is obtained by a subtracting circuit 5. This error signal is multiplied by a prescribed coefficient by a multiplying circuit 4, and supplied to the adaptive filter 1. An MPU 2 adjusts the delay time of the delay circuit 3 or the coefficient of the multiplying circuit 4 according to a received signal intensity (level) from a receiving circuit 6, and the adaptive operation (response) characteristics of the adaptive filter 1 is varied.