Abstract: A silicon resin is applied to the outer wall of the transition piece of a gas turbine subjected to the thermal barrier coating by caulking the cooling holes provided in the inner wall by a resin. Then, the transition piece is heated in an atmosphere furnace in order to burn or decompose the resin. A part of the silicon resin applied to the outer wall of the transition piece is decomposed or evaporated by the heating to be discharged to the atmosphere in the furnace, but a part of the silicon resin remains and protects the outer wall.