PURPOSE: To raise the efficiency of fuel, reduce the cost of fuel, clean up exhaust gas, and increase the power of engine by introducing composite air composed of the vapor of water and ozonized air from an ozonizer into an internal combustion engine.

CONSTITUTION: Ozonized air is introduced through an ozonizer 1 into a highly expanded porous material 4 of vinyl polymer, for example, provided on the bottom of a water container 3 through an air duct 2 by utilizing the suction force of air by means of engine. The composite air composed of molecules F of finely divided ozonized air bubbles formed through the finely expanded porous material 4 and water vapor is introduced at a proper mixing ratio with gasoline into the cylinder through a duct 5 and manifolds, where the ozonized air is quickly expanded and efficiency of combustion is raised. Perfect combustion of fuel can thus be attained, and the enhancement of fuel cost and cleaning of exhaust gas can be attained.