A method and apparatus for detecting pattern defects which includes annularly scanning of a laser beam emitted from a laser light source on a pupil of an objective lens, illuminating the scanned laser beam, through the objective lens, onto a sample on which there is formed a pattern coated with an optically transparent thin film, acquiring an optical image of the illuminated sample, and processing the acquired image to find defects in the pattern. The annular scan diameter of the laser beam is determined based on the thickness of the optically transparent thin film.