There is provided a cylinder head cooling apparatus of an engine capable of enhancing cooling efficiency around an auxiliary combustion chamber wall. The cylinder head cooling apparatus of an engine including a cylinder head having therein an intake port, an exhaust port, an auxiliary combustion chamber, and a cooling water jacket, in which an intake port wall, an exhaust port wall, and an auxiliary combustion chamber wall are placed in the cooling water jacket, the cooling water jacket includes a cooling water inlet and a cooling water outlet, engine cooling water flowed from the cooling water inlet into the cooling water jacket flows out from the cooling water outlet through the cooling water jacket, wherein a cooling water guide wall is provided upstream of the auxiliary combustion chamber wall in a cooling water passing path of the cooling water jacket, and the upstream cooling water guide wall is formed into a shape whose width gradually widens toward a downstream side.