A cylinder head having a plurality of intake ports communicating with the combustion chamber of an internal combustion engine each fixed with a seat ring abutting against an intake valve, wherein intake ports fixed with an eccentric seat ring having the center of inside diameter shifted from the center of outside diameter are mixed with intake ports fixed with a standard seat ring having the center of inside diameter matching the center of outside diameter. A flow coefficient is ensured by the intake ports fixed with a standard seat ring while a swirl flow is enhanced by the intake ports fixed with an eccentric seat ring and thereby contradictory requirements, i.e. insurance of flow coefficient and enhancement of swirl flow, can be satisfied.
