A method of forming a coating film of ceramic material on a surface of an internal member disposed in a vacuum processing apparatus, the surface of the internal member having holes formed therein. The method involves: (A) filling the holes of the internal member with padding plugs, each of which has a core member made from a metal material and a metal-resin composite layer covering the circumferential surface of the core member, the metal-resin composite layer being a complex composed of a metal material and a resinous material exhibiting nonconjugative property to a coating film; (B) forming a ceramic coating film on the surface of the internal member by plasma spraying after step (A); and (C) extracting the padding plugs out of the holes after step (B).