A defect inspection device which inspects for surface defects in substrates, and which includes an illumination section that irradiates the substrate with illumination light having a variable incident angle, and a light-receiving section that receives light from the substrate irradiated with illumination light from the illumination section with a variable detection angle. The light-receiving section receives diffracted light emitted in substantially the same direction as the direction of incidence of the illumination light from the illumination section.