The present invention provides an apparatus for removing the unnecessary thin-film layer on the periphery of the substrate of the plate-like member having a square shape, on the surface of which substrate is formed a thin-film layer. The apparatus comprises a chamber to treat the peripheral part where the peripheral part of the plate-like member is inserted and where the unnecessary thin-film layer on the peripheral part of the plate-like member is removed; and a means to move the plate-like member. The chamber to treat the peripheral part comprises a cover to prevent the scattering of the sprayed particles and the dust for treating the peripheral part, the cover having one of its end-sides that forms a ceiling being closed and having the other end-side that is opposed to the ceiling being open and a suctioning cover for treating the peripheral part, having an opening that has the same shape as the opening of the cover to prevent the scattering of the dust. In the chamber to treat the peripheral part, a blasting nozzle for spraying particles for treating the peripheral part is disposed on the cover to prevent the scattering of the dust, so that the mouth of the blasting nozzle is covered by the wall of the cover to prevent the scattering of the sprayed particles and the dust.