PURPOSE: To shorten the of machining time ranging from boring work to a cylinder inner surface up to the end of honing work by performing an amount of stock removal so much as compared with other parts so as to make an extent of grinding allowance at honing work to the cylinder inner surface become lessened as compared with the other part.

CONSTITUTION: In the finishing of a fine boring, a job for machining to a part L of about one third or so at the lower side of a cylinder block 1 is made later in a boring work head 5 in the axial direction than that to a part H at the upper side from the former. In brief, finishing work after completion of medium finishing, when the boring work head 5 to be situated beneath a cylinder bore is machined as making it rotating and lifting up, an axial feed rate at the lower side part L is delayed. In addition, the feed rate at an upper side part H is accelerated. In brief, an amount of stock removal at the lower side part L is increased as compared with the upper side part H, whereby machining efficiency at the lower side part L is improved.