An inspecting apparatus for a glass substrate detects blurs of a green color filter layer, a blue color filter layer, a column spacer layer, a pixel layer of a thin film transistor, or the like, which are generally hardly inspected. The inspecting apparatus for a glass substrate includes: a first illumination unit supplying reflective light to a surface of the substrate to inspect whether the surface of the substrate is defective or not; a second illumination unit supplying transmissive light from a rear side of the substrate to inspect whether the interior of the substrate is defective or not; a latticed rear plate provided on a rear surface of the substrate; and a driving interferometer system generating a phase difference of light by driving such that a driving guide is moved along the rear plate or the rear plate itself is moved.