A defect inspection system can suppress an effect of light from a sample rough surface or a regular circuit pattern and increase a gain of light from a defect such as a foreign material to detect the defect on the sample surface with high sensitivity. When a lens with a large NA value is used, an oblique detection optics system receives the light from the defect at a reduced elevation angle with respect to the sample surface to reduce light from the sample rough surface, an oxide film rough bottom surface, and a circuit pattern, and increases the amount of the light from the defect and detected. The diameter of a lens is smaller than the diameter of a second lens, resulting in a reduction in the ability to focus the scattered light.