To prevent damage generated through local deformation of a lining steel sheet, a casing body, etc., by connecting the casing body to the lining steel sheet, integrating the casing body, the heat insulation material and the lining steel sheet with each other to provide a hot gas duct of high-temperature preserving structure, and providing a coil-shaped center part of bolts.

A coil-shaped structure 2 is provided in a center part, in which the differential thermal elongation to be generated between a casing body 02 and a lining steel plate 04 is absorbed by a hot gas duct 3 formed by successively arranging from the outside the casing body 02 as a structural member, a heat insulation material 03 to form the heat insulation structure attached to the inside of the casing body 02, and the lining steel sheet 04 which is provided on the inside of the heat insulation material 3 and protects the heat insulation material 03 from the hot gas 09 flowing in a flow passage 010, and the casing body 02, the heat insulation material 03, and the lining steel sheet 04 are integrated with each other by bolts to connect the casing body 02 to the lining steel sheet 04 at each end part. Damage caused by the local deformation of the lining steel sheet 04 and the casing body 02 can be prevented.