Abstract: For identifying an unknown system such as a transmission line or a spatial acoustical coupling, tap coefficients are arranged at taps of an adaptive filter which correspond to a part of an impulse response waveform other than a flat delay part of the impulse response, thus attaining reduction of the convergence time and residual errors without resulting in errors of tap coefficients and tap positions even when a highly nonstationary signal is received. A tap control circuit 91 includes an input signal evaluation circuit 170, which evaluates input signal samples received from delay elements 201 to 20N, sets step sizes to zero and generate a signal for stopping tap position control according to the result of evaluation.