Abstract: The invention provides a liquid fuel irradiated with low radioactivity, method of decreasing the content proportion of noxious ingredients in the exhaust gas of an internal combustion engine, and a method of reduction of fuel consumption by irradiation of liquid fuel with low radioactivity. The irradiated liquid fuel reduces the content proportion of noxious ingredients in the exhaust gas, increases and raises combustion efficiency, pushes the power up, and reduces fuel consumption.