PURPOSE: To improve the wear resistance at a necessary position by hardening only to the necessary position.

CONSTITUTION: In this apparatus, sand cores 2a for casting the needing position to the high wear resistance in a spheroidal graphite cast iron, cooling water passages 3 formed in the inner parts of the sand cores 2a and a means for introducing the cooling water into the cooling water passages 3 when molten iron temp. poured in a mold becomes the eutectic point or lower of the molten iron, are provided. Concretely, the cylinder block 1 is made of the spheroidal graphite cast iron member and a cylinder sliding part of a cylinder bore B is the position needing the high wear resistance.