PURPOSE: To obtain the title apparatus constituted so as to attach a sensor at an angle easy to detect a medium contrast defect to be capable of judging the medium contrast defect as a defect.

CONSTITUTION: A liquid crystal display 3 is arranged on a movable stage 2 and the display pattern generated from a pattern generator 11 is displayed on the liquid crystal display 3 and the movable stage 2 is moved in one direction to read the display pattern by the CCD unit 4 attached above the display pattern on the liquid crystal display 3 and the CCD unit 5 attached obliquely above the pattern. A personal computer 6 compares the read value with a standard pattern to discriminate between a defect and a medium contrast defect.