PURPOSE: An adaptive digital filter is provided to sharply reduce a size by removing a selector between a plurality of blocks having a plurality of taps. CONSTITUTION: An input data delay section(d0-d3) receives input data. The input data delay section(d0-d3) includes a plurality of delay elements which are connected to one another to form a loop. A plurality of counting data delay sections(d0-d15,d'0-d'15) upgrades a counting value based on an operation of output data and an error signal of each stage in the input data delay section(d0-d3). An output data delay section(d''0- d''3) outputs filtered data based on each counting data from the plurality of counting data delay section(d0-d15,d'0-d'15) and the input data. The output data delay section(d''0-d''3) includes a plurality of delay elements which are connected to one another to form a loop.
