With regard to a direct injection diesel engine comprising a piston 11, which has an upper recess constituting a cavity 21, and a fuel injection nozzle 12 injecting fuel into the cavity 12 of the piston, nozzle holes 32, which have at least a plurality of intersecting points between an axis of the fuel injection nozzle 12 and opening direction of the nozzle holes 32, are regarded as a pair, and a plurality of the pairs of the nozzle holes are provided in the fuel injection nozzle 12. An opening of a combustion chamber of the piston 11 is a polygon which has five or more corners. Accordingly, with regard to the diesel engine, engine output is improved, and noise and hydrocarbon in discharged gas are reduced.