PURPOSE: To burn lean mixture fuel in exhaust gas to reduce the emission of detrimental components, by obliquely journalling an exhaust-gas resisting plate in the exhaust pipe of an engine, and as well by providing a retainer plate which presses the plate toward the closing direction of the latter.

CONSTITUTION: An elliptic exhaust-gas resisting plate 2 is obliquely journalled by means of a shaft 3 to a connecting pipe 1 connected to the exhaust pipe (a) of an internal-combustion engine. A resilient retinaer plate 4 which is attached to the exhaust-gas resisting plate 2 to press the exhaust-gas resisting plate 2 in the closing direction of the latter, is received, at its front end, by an adjusting screw 9. Upon acceleration of the engine the exhaust-gas resisting plate 2 slightly opens overcoming the retainer plate 4 to discharge exhaust-gas, however, upon completion of the acceleration the exhaust-gas resisting plate 2 is closed by the retainer plate 4 so that exhaust gas remains in the engine to reduce the discharge of nitrogen oxide and hydro-carbon, and as well the remaining exhaust-gas promotes engine combustion to reduce carbon stuck to the inner wall of the exhaust gas.