PURPOSE: To reduce the fuel consumption rate and to improve the drivability, by feeding the fuel and the air into a pressure container by means of a fuel pump and an air pump while dissolving large amount of air to the fuel in said container and feeding to an internal-combustion engine.

CONSTITUTION: When applying on a gasoline engine, the fuel in a fuel tank 1 is pressure fed through a check valve 3 to a pressure container 4, while the air is pressure fed through a check valve 6 to the pressure container by means of an air pump 5. The amount of fuel and air in the pressure container 4 is maintained constant by comparing each signal from a level sensor 7 for detecting the liquid level of fuel and a pressure sensor 8 for detecting the air pressure with the settings and controlling each pumps 2, 5 in accordance to the difference. When the air pressure is excessive a portion of air is discharged through a safety valve 9. Then the fuel where large amount of air is dissolved in the container 4 is fed through an injection nozzle 10 or an injection valve 11 to a cylinder 12 thus to operate the engine.