1. A defect inspection method for a semiconductor substrate comprising the following steps of: irradiating a surface of an inspected object with the light emitted from an illumination light source; detecting right radiated from the inspected object via a first optical imaging system that has a first optical resolution and at least a second optical imaging system which has an optical resolution lower than the first optical resolution, and imaging a plurality of surface images of the inspected object to be detected; calculating the amount of a first misalignment between a inspection image chosen from the surface images acquired by the first optical imaging system so as to decide and defect and a reference image chosen from the several surface images different from the inspection image; calculating a difference image between the reference image and the inspection image corrected by use of the first optical imaging system to be calculated, and deciding and detecting a defect based on the difference image; storing a first defect information including defect coordinates detected by the first defect detecting step; setting parameters required for calibration to correct a second amount of misalignment produced from the surface images imaged by the first optical imaging system and the second optical imaging system; correcting the inspection image using the second amount of misalignment corrected based on the calibration; deciding and detecting a second defect based on the difference image calculated from the difference between the corrected inspection image and the reference image; and storing a second defect information including defect coordinates detected by the second defect.