PURPOSE: To improve the combustion by preventing the longer injection period in the range with high fuel feed ratio of an injection pump, reducing the initial fuel injection ratio in the range with low fuel feed ratio to suppress the generation of NOx, and improving the air utilization ratio at the bottom part of a combustion chamber.

CONSTITUTION: A nozzle hole of an injection nozzle 1 consists of a main nozzle hole 3 open toward the lower end part of a circumferential wall of a combustion chamber and a sub nozzle hole 4 open toward the bottom part of the combustion chamber in an approximately same phase as that of the main nozzle hole 3. The main nozzle hole 3 is located closer to the tip side of the injection nozzle 1 than the sub nozzle hole 4, and the sub nozzle hole 4 is smaller in diameter than the main nozzle hole 3 to reduce the NOx, the unburnt content or the black smoke to be exhausted from a diesel engine, and the air utilization ratio at the bottom part of the combustion chamber is improved to improve the combustion.