An optical characteristic adjusting apparatus for a laser beam radiation system comprises a transparent substrate which generates visible radiation in response to non-visible radiation, and a stand for positioning the substrate perpendicular to an optical axis of laser beam emitted from a laser beam radiation system. When the non-visible radiation irradiates the surface of the substrate, a bright spot is formed since the visible radiation is generated from the irradiated portion of the substrate. Therefore, an operator can appropriately adjust the optical characteristics of the non-visible radiation at both sides of the transparent substrate since the bright spot can be observed at both sides of the transparent substrate.