At present, it is necessary to suppress the discharge of the toxic substance (especially, NOx and black smoke) in automotive exhaust gas of diesel engine, which is one of the causes of air pollution. And, it is also important to cope with the depletion of the fossil fuel, which is the fuel of the diesel engine. So, in this study, combustion temperature was made to lower by the blending of the oxygenated fuel in gas oil, which was the fuel of diesel engine, and it was tried that the combustion of the fuel which and, it is perfect by the combustion aid action of the oxygen in the oxygenated fuel is promoted.