DEFECT INSPECTION DEVICE FOR PLATE-LIKE TRANSPARENT BODY AND METHOD THEREOF

PROBLEM TO BE SOLVED: To provide a defect inspection device for a plate-like transparent body and a method thereof capable of detecting a minute defect with a length of about 10 μm in a major axis which is present on a surface of the plate-like transparent body without microscope inspection.SOLUTION: In a defect inspection device 10, light-receiving directions of optical receivers 22, 24 are set at a light-receiving angle (0°< ≤60°, preferably 30°≤ ≤45°) having high light-receiving sensitivity to a minute defect which is present on a lower surface of a glass substrate G. Also, output intensity from the projectors 18, 20 is controlled by a CPU such that amounts of illumination lights reaching observation sites by the optical receivers 22, 24 are constant, by which lack of a dynamic range of the optical receivers 22, 24 is compensated for and detection of the minute defect is achieved without signal correction by the optical receivers 22, 24. Further, depth of the minute defect is calculated on the basis of an integrated value of total amount of light received (luminance) detected on both of the optical receivers 22, 24.