PURPOSE: To reduce the quantity of data stored in a memory and to constitute a highly efficient device at a low cost, by storing preliminarily element patterns of a classification for every subsection in a memory and forming a reference pattern on the basis of stored contents.

CONSTITUTION: A substrate 12 to be checked is set on a sample table 10, and the movement of the sample table 10 is controlled by the control signal outputted from a controller 14. Classification data indicating an element pattern of a classification, which each grid has, and conversion indication data are preliminarily stored in the form of a table in accordance with each grid of the substrate 12 in a conversion table memory 18. Plural kinds of element patterns are stored preliminarily in an element pattern memory 20. A conversion control circuit 22 subjects the element pattern to conversion such as rotation or inversion in accordance with conversion indication data and outputs the result to a comparing discriminator 24. The comparing discriminator 24 compares it with the picture signal from an image pickup device 34.