A cylinder head is prepared by integrating an upper cylinder head part and a lower cylinder head part, which are manufactured separately, into the whole, wherein the fuel injector receiving hole, the intake valve stem receiving hole and the exhaust valve stem receiving hole are respectively prepared by integrating their upper portions which are formed together with the upper cylinder head part and their lower portions which are formed together with the lower cylinder head part respectively; the intake duct and the exhaust duct are formed in the lower cylinder head part; the cylinder head water cavity is prepared by integrating an upper water cavity portion formed together with the upper cylinder head part and a lower water cavity portion formed together with the lower cylinder head part into the whole, alternatively, the cylinder head water cavity is formed, as a whole, with the lower cylinder head part.