To eliminate the need for applying an excessively high casting-pressure and prevent the deterioration of aluminum quality in the vicinity of a mold joining surface, when casting a cylinder block having a casting sleeve.

When casting a cylinder block having a casting sleeve, the following are performed: a roughened part 6 having a surface roughness of 50 μm is formed on a fitting face of a water jacket core 5, which is fitted to a bore pin 4 for holding a casting sleeve S, and one end of the roughened part 6 is made to face to a gasket surface g; and further a degassing groove 7 connecting to the roughened part 6 is formed in the outer periphery of the bore pin 4 to release outward compressed gas, air, and the like in a forming space e, which is a dead-end part.