A direct injection diesel engine in which a swirl is produced in a cylinder, comprising: a cavity combustion chamber formed in a middle of a top surface of a piston; a fuel injection nozzle having a plurality of nozzle holes, the fuel injection nozzle disposed at a substantially center position of the cavity combustion chamber; and a glow plug projecting from a ceiling surface of the cavity combustion chamber so that a tip end portion of the glow plug is positioned in the cavity combustion chamber at a piston top dead center position, the fuel injection nozzle having a first nozzle hole group and a second nozzle hole group whose inclination angles (θ1, θ2) with respect to a cylinder center axis line are different from each other, a plurality of first nozzle holes belonging to the first nozzle hole group being arranged so that a spray center axis line of each of the first nozzle holes is a radial shape, a plurality of second nozzle holes belonging to the second nozzle hole group being arranged so that a spray center axis line of each of the second nozzle holes is a radial shape, and the first and second nozzle holes being alternately arranged in a circumferential direction, characterized in that the glow plug is positioned between the spray center axis line of a first nozzle hole and the spray center axis line of a second nozzle hole in the circumferential direction, and projects, in a height direction of the cylinder, up to a height of one of the spray center axis lines (F1, F2) which is directed at a relatively lower side, wherein a nozzle hole diameter of one of the nozzle hole groups is larger than a nozzle hole diameter of the other nozzle hole group, the glow plug is positioned at a swirl downstream side, in the circumferential direction, of the spray center axis line (F2; F1) of a nozzle hole having the relatively large nozzle diameter, and the nozzle hole diameter of the nozzle hole group which is directed at the relatively lower side position is large as compared with the nozzle hole diameter of the nozzle hole group which is directed at a relatively upper side position. a cavity combustion chamber formed in a middle of a top surface of a piston; a fuel injection nozzle having a plurality of nozzle holes, the fuel injection nozzle disposed at a substantially center position of the cavity combustion chamber; and a glow plug projecting from a ceiling surface of the cavity combustion chamber so that a tip end portion of the glow plug is positioned in the cavity combustion chamber at a piston top dead center position, the fuel injection nozzle having a first nozzle hole group and a second nozzle hole group whose inclination angles (θ1, θ2) with respect to a cylinder center axis line are different from each other, a plurality of first nozzle holes belonging to the first nozzle hole group being arranged so that a spray center axis line of each of the first nozzle holes is a radial shape, a plurality of second nozzle holes belonging to the second nozzle hole group being arranged so that a spray center axis line of each of the second nozzle holes is a radial shape, and the first and second nozzle holes being alternately arranged in a circumferential direction, characterized in that the glow plug is positioned between the spray center axis line of a first nozzle hole and the spray center axis line of a second nozzle hole in the circumferential direction, and projects, in a height direction of the cylinder, up to a height of one of the spray center axis lines (F1, F2) which is directed at a relatively lower side, wherein a nozzle hole diameter of one of the nozzle hole groups is larger than a nozzle hole diameter of the other nozzle hole group, the glow plug is positioned at a swirl downstream side, in the circumferential direction, of the spray center axis line (F2; F1) of a nozzle hole having the relatively large nozzle diameter, and the nozzle hole diameter of the nozzle hole group which is directed at the relatively lower side position is large as compared with the nozzle hole diameter of the nozzle hole group which is directed at a relatively upper side position.