A direct injection diesel engine includes a piston having a reentrant cavity and a multi-hole fuel injection nozzle disposed on a center line of the cavity. The cavity is formed by a lip portion defining a smallest diameter at a position below a piston crown surface and a raised portion formed at a center of the bottom and shaped like a frustum of a cone. A conical surface of the raised portion is formed to have an angle pointing to a spray point of the fuel injection nozzle at a piston top dead center position. The height position of a top surface is substantially equal to the height position of the lip portion. This structure is to promote the oxidation of soot by utilizing the air in the central part of the cavity.