To provide a novel structure for suppressing flow resistance of cooling water while utilizing latent heat cooling for improving the efficiency of cooling a cylinder head.

A latent heat cooling chamber 20 is formed to cover the outside (the upper face) of a heat source portion of a combustion chamber 4 or the like, and a cooling water channel 41 is formed for the latent heat cooling chamber 20 across a partition wall 43. The cooling water flows along the upper face of the partition wall 43 not along the outer face of the heat source portion. The shape of the partition wall 43 is independent of the complicated shape of the heat source portion. The existence of the latent heat cooling chamber 20 permits good cooling operation near the heat source portion, while proper shape design of the partition wall 43 suppresses flow resistance.