PURPOSE: To enhance the combustion efficiency and as well as prompt the burning time by a method wherein a different kind of fuel having low flashing point is precedently burnt and as well as the combustion energy of said precedently burnt fuel is used as the priming source of diffusion combustion of atomized fuel particles, realizing consequently the time-staggered combustion.

CONSTITUTION: Heavy oil is fed from a heavy oil tank 1 into a stirrer 3 and on the other hand 3W5% gasoline basing on the amount of the heavy oil is fed from a gasoline tank 2 into the stirrer 3 while being controlled by a throttle valve 13 in order to be stirred and mixed with each other by means of a motor 4. When said mixed fuel is jetted from the injection nozzle 15 of a burner 10, at first the gasoline, which is low in flashing point, is primarily burnt and, after that, the heavy oil is secondarily burnt due to the priming action of the primary combustion of the gasoline and consequently completely burnt. In such a manner as mentioned above, the complete combustion of the fuel and the reduction of the burning time can be realized, resulting in improving the combustion efficiency.