PURPOSE: To provide a poppet damper of an exhaust gas duct having a high sealing performance by following up a thermal deformation in which the processing of a sealing surface is easy.

CONSTITUTION: A poppet damper comprises a damper sheet 2 provided in a duct casing 1, a poppet plate 3 for controlling the flow of exhaust gas by regulating a gap to the sheet 2, and an air cylinder 7 and a damper shaft 6 for driving to reciprocating the plate 3, wherein the plate 5 is mounted at a specific gap at the plate 3, and at the time of closing, the plate 5 is brought into close contact with the sheet 2. The thickness of the plate 5 is preferably 0.3-1.0mm. A space 4 having a thickness of 0.5-2.0mm is interposed between the plates 3 and 5 to form a specific gap.