A device for inspecting a polycrystalline silicon layer that is crystallized by receiving irradiated laser beams on a front side of the polycrystalline silicon layer includes: a light source configured to emit inspection beams to a rear side of the polycrystalline silicon layer; a light inspector configured to inspect the inspection beams reflected at the rear side of the polycrystalline silicon layer; and a controller that controls the light source and the light inspector.