PURPOSE: To obtain a folded plate wherein the remaining of an air-layer between a metal plate and a thermal insulating material is prevented by placing the rear of a tape upon one side of the metal plate to stick, and corrugating the thermalby insulating material formed of an abhesive tape and thermally insulat ing sheets.

CONSTITUTION: Adjacent edges of a plurality of thermally insulating sheets 21 are butted to arrange, and an adhesive tape 22 is laid across both butt edges of the surfaces of the thermal insulating sheets 21 to connect them to each other. At that time, a thermally reactivating type adhesive layer is provided to the rear of the adhesive tape 22, the thermally insulating material 12 is stuck on the metal plate 11, and the adhesive tape 22 is surely made to adhere to the metal plate 11. Remaining of an air-layer between the metal plate 11 and thermal insulating material 12 is prevented, and the thermally insulating material is folded in the shape of a wave.