To rapidly and completely remove hydrocarbon consisting essentially of methane without the need for another catalyst, etc., by oxidation cracking the hydrocarbon in gas containing the hydrocarbon consisting essentially of the methane of high temperature by using ozone.

The previously formed ozone is added to the high-temperature gas in the case the hydrocarbon in the high-temperature gas ≥37°C containing the hydrocarbon consisting essentially of the methane is removed by oxidation cracking. At this time, the ozone is previously formed from air, oxygen-enriched air, oxygen as well as exhaust gases in which oxygen is included, etc. Such ozone is added to the gas containing the hydrocarbon consisting essentially of the methane. For example, the ozone is added to the gas exhausted from the cylinders of a gas engine to remove the hydrocarbon in the gases by oxidation cracking. The treated gases are supplied to a turbine to drive the turbine and are then discharged. The amount of the ozone to be added is most adequately regulated according to the temperature and velocity of the exhaust gases.