PURPOSE: To reduce deformation due to thermal expansion during processing of a cylinder hole, and to perform the process with good accuracy by performing grinding process of a cylinder by a honing grinding stone, letting a fluid cooling medium pass in a tube passage of a cylinder block.

CONSTITUTION: During the grinding of a cylinder hole 6 by a honing grinding stone 9, cooling water in a tank 12 is circulated and supplied into a water jacket 7 which is formed in a cylinder block 5 to be ground, by a pump 13 of a circulation device 11. The block 5 is sufficiently cooled thereby, so as to reduce frictional heat caused by the grinding process. Deformation due to thermal expansion is reduced, and the cylinder hole 6 of the cylinder block 5 is ground and processed with a high roundness.