PURPOSE: To burn an unburnt HC, CO or the like perfectly, in the internal combustion engine of a constant volume cycle or diesel cycle.

CONSTITUTION: The concentration of oxygen in an exhaust gas is detected by a sensor 16 and the opening closing of an oxygen measuring valve 8 is controlled by an electronic controller 19 based on the fuel injection amount of an injector 13 and the oxygen stored in a low temperature tank 11 is sent to an oxygen suction chamber 2 through a low pressure valve 10 and supplied to the combustion chamber 18 of the engine from an intake valve 6 through a forced mixing chamber 3 and a tubulent flow mixing chamber 4.