To manufacture a sealing device used for a coupling part of a duct to an annular part thermally elongated, at a low cost.

An annular recessed portion 20 is formed outward on an outer-periphery surface of one end of a diffuser inner tube 2 as the duct. A leaf spring 22, a ring plate 23, and a seal rope 21 are sequentially disposed in the recessed portion 20. The seal rope 21 is pressed against an inner-periphery surface of a gas turbine exhaust outlet portion 1 as an annular portion. The seal rope 21 impregnated with carbon is disposed in an annular manner. The ring-shaped plate 23 has a cut end portion on it and can be expanded and contracted in the diametrical direction. The leaf spring 22 is formed in a zigzag shape and curved into a ring shape to be disposed.