A method and apparatus for detecting defects are provided for detecting harmful defects or foreign matter with high sensitivity on an object to be inspected with a transparent film, such as an oxide film, by reducing noise due to a circuit pattern. The apparatus for detecting defects includes a stage part on which a substrate specimen is put and which is arbitrarily movable in each of the X-Y-Z-θ directions, an illumination system for irradiating the circuit pattern with light from an inclined direction, and an image-forming optical system for forming an image of an irradiated detection area on a detector from the upward and oblique directions. With this arrangement, diffracted light and scattered light caused on the circuit pattern through the illumination by the illumination system is collected. Furthermore, a spatial filter is provided on a Fourier transform surface for blocking the diffracted light from a linear part of the circuit pattern. The scattered and reflected light received by the detector from the specimen is converted into an electrical signal. The converted electrical signal of one chip is compared with that of the other adjacent chip. If these signals are not identical to each other, the foreign matter is determined to exist on the specimen in detection.