PURPOSE: To raise the efficiency of combustion by injecting water into air intake pipe in the form of atomized state by exhaust pressure and the nagative pressure of air intake pipe.

CONSTITUTION: Exhaust pressure exerts on the water tank 4, water is supplied through a conduit from the water supply pipe 5 to the water tank 9, and water is then supplied to the discharge pipe 27. On the other hand, the sucked air is flowed through the shaft piping 20 and the air injection pipe 14 into the injection cylinder 13, and the incoming air absorbs water from the discharge pipe 27 and then is injected conically into the injection cylinder 13. In this case, the amount of water absorbed in the incoming air is proportional to the flow rate of air passing through the outlet of the discharge pipe 27 and the flow rate of air is varied with the relative position between the trough hole 23 of the movable disk 24 and the through hole 21 of the fixed disk 22. In short, when the movable disk 24 turns to close the through hole 21 of the fixed disk 22, air is supplied concentratively to the air injection pipe 14 alone and the amount of water absorbed from the discharge pipe 27 is therefore increased. The movable disk 24 is interlocked with accel pedal.