PURPOSE: To improve the combustion efficiency and the output by producing minus ion through catalyst reaction to be produced in the magnetic field between the opposite poles of a magnet with respect to the intake air then decomposing into minus oxidizing ion and feeding to a carburetor.

CONSTITUTION: A porous resin air-filter 3 of super micro particles and a plurality of magnets 4 covered with noncombustible urethane 5 are inserted into a tubular heat-resistant case 2 having a vent 1 to construct a catalyst oxygen producer A. Oxygen produced here is led through a conduit 7 having an orifice 6 at the intermediate section to a foam producing body 9 arranged in the water in a container 8 of a foam producing device B thus to produce water foam. The water foam is finely decomposed on the water face to produce micro particle spray 10 which is led through a conduit 11 into a flexible tube 13 wound over an exhaust tube 12 and a cover 15 for utilizing the excessive heat to produce vapor which is fed to an intake manifold.