SURFACE DEFECT INSPECTION DEVICE

PURPOSE:To extract band-shaped defect generated continuously in a direction which is vertical to the direction of a light-reception element of a line sensor from a threshold reference signal. CONSTITUTION:An average light quantity distribution signal of the entire surface of a body to be inspected is generated by a threshold reference signal measuring device 60. The average light quantity distribution signal is subjected to differential processing for two times by an operation device 70, the light-quantity distribution according to an optical system is eliminated, only the signal component of a low-frequency defect part which is 10mm or longer in width is emphasized and left, and defect extraction according to a certain threshold is performed by the threshold method, thus obtaining a defect detection signal 80 and hence extracting a band-shaped low-frequency defect generated continuously in the direction which is vertical to the direction of the light-reception element of a line sensor.