PURPOSE: To suppress exhaust gas and to improve the combustion efficiency by providing a metal box made by laminating metal meshes composed of β-radioactive alloy then lining thin board composed of β-radioactive element between an air suction port and carburetor of internal-combustion engine.

CONSTITUTION: Metal meshes composed of β-radioactive element (or isotope) for emitting β-ray or β-radioactive element alloy mixed with said β-radioactive element are provided in a tubular metal box placed between an air inlet port (or an air-cleaner) of an internal-combustion engine and a carburetor (or supercharger). The inner wall face of said metal box is lined with a thin board composed of β-radioactive element to prevent the air to be sucked into the combustion chamber from reaching to the carburetor (or supercharger) except when passing through the metal mesh composed of said β-radioactive element.