A method for etching doughnut-type glass substrates, which comprises
laminating a plurality of doughnut-type glass substrates each having a
circular hole at its center so that the circular holes form a cylindrical
hole, and applying an etching treatment to inner peripheral edge surfaces
of the plurality of the laminated doughnut-type glass substrates all at
once by means of an etching liquid or an etching gas, wherein the etching
liquid or the etching gas is supplied from one end of the cylindrical
hole, made to flow in the cylindrical hole, and discharged from the other
end of the cylindrical hole so that it is not in contact with exposed
main surfaces of the doughnut-type glass substrates at both ends of the
laminate consisting of the doughnut-type glass substrates.