Where a thin film formed on a glass substrate is etched with a solution containing a fluoride, insoluble residues formed by the reaction of the solution with glass substrate components adhere to the back of the substrate to cause etching non-uniformity called roller marks. So, a solution is supplied directly to supporting members for supporting the glass substrate, or concentratedly to a region where the substrate and the supporting members come into contact and from a position opposite to the transporting direction of the substrate, or to both the supporting members and regions where the substrate and the supporting members come into contact. This enables the roller marks to be kept from forming, consequently making it possible to improve display quality of display devices.