PURPOSE: To shorten inspecting time without reducing defect detecting sensitivity by providing plural lenses, detectors, and image memories, and processing the fetching of pattern data on a photomask in parallel.

CONSTITUTION: Two light sources 10 and 22, lenses 9 and 21, detectors 5 and 23, and defect memories 6 and 24 are provided, respectively, and respective intervals of the light sources 10 and 22, and the lenses 9 and 21 can be set based on the size of an inspecting area. The detector 23 and the image memory 24 detect and store a pattern image on the photomask 13 fetched from the lens 21. The image memories stored in the memories 6 and 24 are alternately sent to a comparator circuit 7, data stored in the data memory 4 are compared with the image data at the circuit 7, only different point is sent to the defect memory 8, and the data is stored. Consequently, the inspecting time can be shortened to half, and the defect detecting sensitivity is not reduced by possessing two lenses.