PURPOSE: To easily detect a defect in the pattern of a substrate by superposing a mask which has a light reflecting part at a part corresponding to the light shied part of the substrate and a light transmission part at the remaining part and irradiating the substrate from its reverse surface.

CONSTITUTION: The pattern which has the light shield part 16 is formed on the light transmissive substrate 12. The mask 14 which has the light reflection part 18B corresponding to the light shield part of the pattern and the light transmission part 18A as the remaining part is superposed on the substrate 12. The mask 14 is irradiated with light from above and the substrate 12 is also irradiated with the light from its reverse surface side. At this time, if the pattern has a defective part through which the light is not transmitted, the part becomes dark. Then, a decision circuit decides the quantity of light from the mask 14 to inspect whether there is a defect or not. Thus, the mask having the light reflection part and light transmission part corresponding to the substrate of the substrate is superposed on the substrate, so a defect in the pattern is inspected at a high speed with high accuracy.