JP2792703B

PURPOSE:To easily execute an identifying operation by dividing each density value by the total sum value of the respective density values, calculating the arrangement pattern of density strength at a part detected by a detection sensor and comparing the arrangement pattern with a reference pattern determined in advance. CONSTITUTION:A CPU 41 is equipped with an average value calculating means 412, density value calculating means 413, density total calculating means 414, normalizing means 415, comparing means 416, discriminating means 417 and other arithmetic and control means 418. The average value of data stored in a storing part is calculated and difference between the average value and the data is calculated as the density value. Then, the total sum value of the respective density values calculated by the density value calculating means 413 is calculated. Each density value is divided by the total sum value and the arrangement pattern of the density strength at the part detected by the detection sensor is calculated. Based on the result of comparison between the arrangement pattern and the reference pattern determined in advance, paper sheets are discriminated. Thus, the identification is made easy.