PURPOSE: To efficiently detect a pattern defect, by a method wherein an enlarged negative plate to be a master and a formed pattern are optically overlapped with each other, and quantities of light passing therethrough are detected.

CONSTITUTION: The pattern formed on a transfer mask 1 is displayed on a CRT display 5 through an magnifying lens system 3 and a TV camera 4. In addition, the pattern on a reticle 2 for magnifying the pattern on the transfer mask 1 is overlapped with the pattern on the CRT display 5. The whole of the resultant image of the overlapped patterns is scanned by means of a photoelectric detecting element to measure and compare luminous intensities at various positions on scanning lines with each other. Any pattern defect on the mask or reticle can be recognized as a bright part or dark part.