The periphery of an area of a master pattern is expanded by a required number of pixels to define a plurality of master pattern areas two-dimensionally misregistered pixel by pixel, for performing pattern comparison of the respective master pattern areas with an area of an object pattern. The object pattern is deemed defective when all of the comparisons indicate pattern mismatches. The pattern is deemed not defective when at least one comparison indicates a pattern match. Thus, even if an inspected object includes misregistration errors, pattern defects can be detected with high accuracy.