PURPOSE: To cancel quickly an echo signal by setting a constant of division obtaining an approximated estimate impulse response correcting amount of an echo cancellor so as to satisfy a prescribed inequality.

CONSTITUTION: An input signal (x) from a 4-wire section is fetched in an (x) register 17 and a time series signal xj of the signal (x) is inputted to a convolution circuit 18, a multiplier 21 and a square accumulating circuit 23. The circuit 18 applies convolution between the signal xj and an estimated impulse response H'j from an H register 19 and outputs an estimated echo signal y'. The signal y' is subtracted 16 from an actual echo signal (y) and its residual difference ej is inputted to a terminal station 11 and the multiplier 21. The multiplier 21 inputs the result of multiplication among signals e, xj and correcting coefficient α to a shift register 22. A (k) discriminating circuit 24 discriminates a (k) satisfying an inequality from a signal xj2 from the circuit 23 and the coefficient α, a control circuit 25 shifts the register 22 by k-bit by using the (k), outputs an approximated value ΔH'j of an estimated impulse response correcting amount and inputs the value to an adder 26. The adder 26 adds the signals H'j and ΔH'j and outputs an impulse response H'j+1 at next time.