PURPOSE: To prevent the locally high temperature heating an outer cylinder part from occurrence by stopping an outer flange of an inner cylinder part peripheral surface to an inner flange of an outer cylinder part internal peripheral surface, and forming a sloped surface in a direction of separating from the inner cylinder part peripheral surface in a partial or total part of an inner flange internal peripheral end face.

CONSTITUTION: A sloped surface 16, in a direction of separating from a peripheral surface 2a of an inner cylinder part 2, is provided in an internal peripheral end face 10a of an inner flange 10. The inner cylinder part 2 is heated by a high temperature fluid A, circulated in an inner cylinder 1a and the inner cylinder part 2, and placed in a high temperature condition, to transmit high temperature heat of the inner cylinder part 2 to an outer cylinder part 3 through flanges 9, 10, and also heat flux, by radiation heat radiated from the inner cylinder part 2, tends to be transmitted to the inner flange 10 of the outer cylinder part 3 through a heat insulating material 12. However, by cutting off an internal peripheral side angular part of the inner flange 10, a heating value of the heat flux, transmitted to the inner flange 10, is limited, to prevent a part, brought into contact with the inner flange 10, from being easily locally high temperature heated. Accordingly, causing thermally deforming and cracking the outer cylinder part 3 due to local heating can be prevented.