PURPOSE: To improve the echo cancelling capability by constituting a double integration circuit in realizing a tap coefficient algorithm by the least mean square(LMS) method.

CONSTITUTION: The titled filter consists of a tapped delay line 1 where an input signal is retarded more while the signal goes toward the poststages, a multiplication means 5 multiplying each tap of the delay line 1 with an error component between a filter output and a reference signal, a leak integration means averaging the input being the result of multiplication means from the means 5, a complete integration means 3 receiving an output of the means 4 for generating a filter coefficient, a multiplication means 2 multiplying a tap coefficient being an output of the means 3 with each tap, and an adder means 6 summing the tap coefficients of each tap and the result of multiplication totally. Since the tap coefficient is corrected according to the quantity averaging the mean of set by constituting the double integration circuit in this way, the noise or echo cancelling capability in the presence of a sound signal component in a canceller input signal is improved and the converging characteristic in the presence of the sound component is improved.