PURPOSE: To improve the stability of ignition and the propagation of a flame by forming external shape of a valve shaft part asymmetrically about the center of a poppet valve and drive-rotating it in accordance with an operational condition so as to increase distribution of fuel in the vicinity of a spark plug at the time of at least low load operation.

CONSTITUTION: When a poppet valve 4 is opened by a solenoid 6, supplied fuel to a passage 7 from a fuel supply valve 8, while being mixed with pressure air supplied to the passage 7 from an air introducing hole 12, is energetically jetted from the point end of a nozzle part 3. Here a flow amount is increased in a side of larger passage sectional area in the periphery of the valve 4, and a fuel atomized amount from a nozzle part 2A is increased in a side of larger sectional area of the passage 7 as shown by a two-dot chain line. Accordingly, by holding the valve shaft part 4A of the valve 4 in a rotational position apart from a spark plug 27 by a control circuit 35, during low speed/low load operation a region E toward the spark plug 27 is enlarged in a jet flow to a combustion chamber 19 from the passage 7 with ignitability stabilized simultaneously with stratified combustion performed by uniformly propagating a flame.