An inspection method for an illumination optical system of an exposure tool includes coating a surface of an exposure target substrate with a resist film; placing a plurality of imaging components deviating from an optical conjugate plane of a surface of the resist film; generating a plurality of inspection patterns of the resist film having a plurality of openings, by projecting exposure beams output from a plurality of effective light sources onto the resist film via the imaging components; measuring one of the inspection patterns as a reference image, and processing the reference image so as to provide reference image data; and determining an abnormal inspection image by measuring inspection images of the inspection patterns and comparing a plurality of inspection image data provided by processing the inspection images with the reference image data.