PROBLEM TO BE SOLVED: To form a rough surface by easily exposing coarse granular material partially from a resin coating film surface and solidifying it even when a thickness of a covering plate or the like is less than 3 mm.SOLUTION: In a method of forming a rough surface on a metal thin plate, a resin coating film of thermoplastic resin is formed on a thin metal substrate, the metal substrate with the resin coating film formed is mounted on a heating plate, a molten state of the resin coating film is maintained by heating by the heating plate, inorganic coarse granular material in a heated state is sprayed and adhered on the molten resin coating film, the metal substrate is released from a mounted state on the heating plate, and the resin coating film in a state that at least a part of the inorganic coarse granular material is exposed from a surface of the resin coating film is cooled and solidified.
