A diesel engine comprises: a cylinder head covering one end of a cylinder; a piston having a crown surface opposed to the cylinder head, and performing a reciprocating movement within the cylinder; and a fuel injector attached to the cylinder head. The cylinder head is formed with an intake port so as to generate a swirl flow within the cylinder. The crown surface of the piston is formed with a cavity which is recessed toward an opposite side of the cylinder head and which has a circular shape in planar view, and a notch which is recessed radially outward from a peripheral edge of the cavity. The fuel injector is formed with an injection hole oriented toward an inside of the cavity.