In a defect inspection apparatus for inspecting a wafer provided with a circuit pattern for defects, the illuminating direction of illuminating light rays is selectively determined such that an area containing a defect that scatters light of high intensity coincides with the aperture of a dark-field detecting system, and such that regularly reflected light regularly reflected by a pattern, which is noise to defect detection, does not coincide with the aperture of the dark field detecting system.