PURPOSE: To prevent the generation of crack by depositing a heat resisting material in the circular cavity formed between an intake and an exhaust valve seats on the lower surface of a cylinder head, between said valve seats and a fuel injection nozzle bore and between said nozzle bore and the side wall surface of said cylinder head.

CONSTITUTION: A cylinder head 1 is provided with an intake valve seat 2, an exhaust valve seat 3 and a fuel injection nozzle bore 4. A circular cavity 6 with a radius (r) is formed on the lower surface of said cylinder head 1 in such a manner that its center point (o) is approximately equal to the center of the triangle formed by linking the centers of said intake and exhaust valve seats 2, 3 and said nozzle bore 4 and it includes the portion between said nozzle bore 4 and the side wall surface 1a of said cylinder head 1. In said circular cavity 6, a heat resisting material is thermally sprayed and deposited in laminar. Thus, the one circular heat resisting material layer 5 is able to give heat resistance to such portions liable to generate cracks, due to the influence of a heat load.