by a predetermined step size u03b4 to scale down a resultant of the multiplication the resultant of the multiplication is renewed into a new coefficient of the tap by being added with the present coefficient of the tap stored in the coefficient storage memory 11c 4 in the adder 11c 3 and transmitted to outwardly and stored in the coefficient storage memory 11c 4 for the next tap coefficient calculation in this case even if an s number of bits are required for the digital filter each of the coefficient renewing parts 11c1 11cn uses the s number of bits together with a p number of bits expanded to an lms side in the coefficient storage memory 11c 4 for stability and exactness sake in the coefficient renewal that is the total number of bits used in the coefficient renewal is s p bits fig1 illustrates a detail system of a second embodiment of the digital filter shown in fig5 an embodiment of a coefficient renewing circuit simplified in comparison to the first embodiment wherein the filter coefficient renewing equation is further simplified utilizing size and negative positive polarity information of an error signal and size and negative positive polarity information of a data referring to fig1 the second embodiment filter 11 includes data memories.