An alkaline etchant containing a quaternary ammonium hydroxide, water, and an inhibitory substance for inhibiting contact between hydroxide ions generated from the quaternary ammonium hydroxide and objects P1 to P3 to be etched is prepared. The prepared etchant is supplied to a substrate in which the polysilicon-containing objects P1 to P3 to be etched and objects O1 to O3 not to be etched, which are different from the objects P1 to P3 to be etched, are exposed, thereby etching the objects P1 to P3 to be etched while preventing the objects O1 to O3 not to be etched from being etched.