Cooling structure of cylinder head and method for manufacturing cylinder head

In a cylinder head (2), a cooling water passage (12) with a circular shape (an elliptical shape) in cross section in radial direction is formed at an area (11) (lower layer deck) closer to a combustion chamber (4) than a water jacket (9) in which a cooling water flows. The cooling water passage (12) of the cylinder head (2) is formed by casting by providing a hollow core (14) in a mold (16) and removing the hollow core (14).