A surface image of a semiconductor wafer having a defect is picked up as a inspection image while a surface image of a semiconductor wafer having no defect is stored in an image memory as a reference image. A density difference image between the inspection image and the reference image. By extracting the defect in wiring and non-wiring regions from the density difference image, extract images are obtained. Two luminance information for wiring and non-wiring regions are obtained from extract images. Based on the luminance information, the type of the defect is determined and a production process where the defect has occurred is detect.