With the center position CP of a support shaft 6 supporting a grinding wheel 4 being a reference, a provisional grinding start position S0′ for a first workpiece 2 is calculated, based on a diameter ID of the first workpiece 2 before grinding, a diameter WD of the grinding wheel, a grinding completion position S4 on the first workpiece after the grinding, and an actual grinding start position S0 of the grinding wheel before grinding in second and subsequent grinding. S0 is determined by performing the grinding by moving the grinding wheel from S0′ and by moving the grinding wheel away from the first workpiece by a distance corresponding to S4 near the grinding completion position S4. S0′ is set by a calculation, S0′=ID−WD−S4−Sα, considering an allowance Sα between S0 and S0′.