PURPOSE: To extract pattern features with a small number of data bits, by using the frequency distribution, which is indicated by respective appearance frequencies of small area information distribution patterns, as pattern recognition information.

CONSTITUTION: When an output terminal B>A of a comparator CMP2 becomes 0, this signal is applied to an input terminal IN of a shift register SR2, and signal "0" indicating an inverted h>h1 is shifted bit by bit at every time the clock signal is inputted. A counter CO9 is counted up successively to select successively input terminals I1WI8 of a multiplexer MX1, and values of h1Wh8 are inputted to an input terminal B of the comparator CMP2, and the result from the comparison of B>A (hn>inverted h) is inputted to the register SR2 successively. If the clock signal is inputted when the counted value of the counter CO9 is 7, 8-bit feature data b1Wb8 are held in the register SR2, and 16-bit overall feature data is extracted to a shift register SR1.