The present invention provides a variety of optical functions so as to be applicable to various kinds of objects to be inspected. For each of the optical functions, the invention accumulates contrasts (brightness differences), etc. of defects to be detected (DOI) and false defects not to be detected (nuisance), and efficiently selects parameters advantageous for inspection with high sensitivity and low nuisance ratio. A wavelength band, an illumination scheme, and filtering parameters can be selected for an optical system.