To cool exhaust air and reduce concentrations of carbon monoxide and carbon dioxide contained in the exhaust air without preventing backflow of outside air from a secondary exhaust pipe due to effects by wind etc.

A primary exhaust pipe 2 arranged on the upstream side of exhaust air G and the secondary exhaust pipe 3 arranged on the downstream side of the exhaust air G are separated from each other, and a baffle structure is provided between the primary exhaust pipe 2 and the secondary exhaust pipe 3. A baffle plate 5 having cut parts 5c formed partially to allow the exhaust air G to pass through without change is arranged to oppose to an end port of the primary exhaust pipe 2. The secondary exhaust pipe 3 is formed to be larger than the primary exhaust pipe 2 and deeply covered in the axial direction of the primary exhaust pipe 2 via a clearance with the outer side of the primary exhaust pipe 2.