1. A defect inspection method for a semiconductor substrate comprising the following steps of: irradiating a surface of an inspected object with light emitted from an illumination light source; detecting light 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 an amount of a first misalignment between an inspection image chosen from the surface images acquired by the first optical imaging system and a reference image chosen from the several surface images different from the inspection image; deciding and detecting a defect based on the reference image and the inspection image corrected in accordance with the calculated amount of the first misalignment by use of the first optical imaging system; 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 corrected inspection image and the reference image; and storing a second defect information including defect coordinates detected by the second defect.