PURPOSE: To absorb inclination of a shaft by means of a gap between the outer periphery of a shaft and the inner periphery of a seal member during inclination of the shaft by forming a spherical seal surface on at least one of one end side of the seal member and a body, and bringing the seal surface into contact with the other.

CONSTITUTION: An exhaust valve device located at the branch part of an exhaust passage 2 (,3) rotatably supports a shaft 11 through bearings 10... in a mounting hole 9 formed in a body 7 with a gap S1 between the outer periphery of a shaft 11 and the inner periphery of the bearing 10. A shut-off valve 13 is mounted on one end side of the shaft 11 through a mounting member 12 and a seal member 16, such as a gasket, is arranged on the periphery of the shaft 11 in the vicinity of a flange 15 formed on the other end side of the shaft 11. The seal member 16 has one end side 16a formed in a round shape and brought into contact with a recessed spherical part 17 formed in the body 7. The plane-form other end side 16b of the seal member 16 is brought into contact with the flange 15.