To reduce or prevent the cross talk of adaptation against noise or adaptation by noise by selecting the size of a valid step in accordance with the non-linear function of the instantaneous noise ratio against a signal of an input signal.

An adaptive FIR filter AF decides estimation (y)(n) against a signal (d)(n) (near end speaker)+echo) from a stochastic input signal (x)(n) (far end speaker). Optimum reference for estimation (y)(n) satisfies relation that the square of an error signal (e)(n)=d(n)-y(n) is minimum. Then, d(n) and y(n) are inputted to an adder S for deciding the error signal. In such a case, it is desirable to select a coefficient like c2=0...1, c3=1...2. Noise power is obtained by measuring the power of the signal d(n) in the halt of conversation in the signal x(n) by a low pass filter.