An inspection device is required to detect a minute defect, that is, to have high sensitivity as semiconductor devices become finer. There are some approaches for improving the sensitivity. One is to shorten the wavelength of illuminating light radiated onto a sample. This is because, assuming that the wavelength of the illuminating light is λ, I∝λ−4 is established between the magnitude of scattered light is I and λ. Another approach is to use illuminating light including multiple wavelengths. An approach for taking in more scattered light generated from the sample is also possible. However, an optical system suitable for these approaches has not been sufficiently found in conventional techniques. One feature of the present invention is to detect a defect by using a Wolter optical system including a Wolter mirror.