PURPOSE: To stably detect scratches and foreign matters even when the fluctuation of brightness and the slight deviation of positions and angles are present by measuring the degree of the variation of density values in picture elements due to the position and angle deviation of reference pictures or the like and reducing the size of an error corresponding to a distribution value in picture elements.

CONSTITUTION: In addition to an error detection part 7 for detecting the size of the error of the picture element unit for which the fluctuation of the brightness between an object picture memory 1 and a reference picture memory 2 is corrected and outputting a signal corresponding to the value of the error, this processor is provided with a reference picture distribution memory 8 for storing the distribution of the density values in picture elements in the memory 2 and an error correction part 9 for correcting the output of the detection part 7 based on the value of the memory 8. Then, the distribution value which is the degree of the variation of the density values of the picture elements in picture elements is measured and stored in the memory 8 before executing inspection and the size of the error of the detection part 7 is corrected by the correction part 9 so as to be reduced corresponding to the distribution value in picture elements at the time of executing the inspection. Thus, the part of the scratches and foreign matters and the other parts can be easily separated.