PURPOSE: To improve fuel consumption and the exhaust gas purification performance by feeding the steam of the aqueous solution of bvbalent/tervalent iron salt or the like to the combustion chamber of an internal combustion engine.

CONSTITUTION: An aqueous solution tank 2 is connected to an air duct 9 at the position near the combustion chamber on an air intake passage from an air cleaner 1 to the combustion chamber 6, a ceramic body 8 heated by an electric heater 3 and generating far infrared rays is arranged in it. The aqueous solution of bivalent/tervalent iron salt, or the aqueous solution of the bivalent/ tervalent iron salt compounded material made of bivalent/tervalent iron salt and a zinc group metal compound, or the aqueous solution of the inorganic or organic compound or compounded material using bivalent/tervalent iron salt as a base is stored in the aqueous solution tank 2. The steam generated when this aqueous solution is heated is fed to the combustion chamber 6, thereby the combustibility of fuel is improved.