A direct-injection diesel engine comprising a cylinder block having a cylinder in which a piston is slidably received, a cylinder head connected to an upper surface of the cylinder block, a fuel injector nozzle mounted on the cylinder head to directly inject fuel into a combustion chamber defined between the piston and the cylinder head, and first and second independent intake ports provided in the cylinder head for introducing intake gas into the combustion chamber. An intake controller is mounted in the second intake port for bringing the second intake port into a controlled intake gas flow state in a region of low speed operation of the engine and into a normal state in a region of high speed operation of the engine. Each of the first and second intake ports are formed helically in the same direction to produce swirls in the same direction in intake gases introduced respectively through the intake ports into the combustion chamber.