Abstract: A pair of intake ports and a pair of exhaust ports corresponding to respective cylinders in a multi-cylinder engine are formed in a cylinder head. A water jacket is formed which recirculates cooling water around the ports in the cylinder head. A side wall of the intake port of one cylinder and a side wall of the exhaust port of another cylinder adjacent to the first cylinder, are connected by a rib formed on the base surface of the water jacket. The rib cuts transversely across a straight line joining the centers of the two cylinders. In this way, the rigidity of the cylinder head is increased, seal tightness of a join between the cylinder head and a cylinder block is improved, and the cooling water in the water jacket is recirculated around the exhaust ports which bear high thermal load.