A workpiece 23 formed of a circular thin plate is rotated about its center as an axis L1. Each of disk-shaped rotating grinding wheels 27 and 28, while being rotated about an axis L3 extending in a direction substantially parallel to the plane of the workpiece 23 and perpendicular to the radial direction of the workpiece 23, is made to undergo relative feeding movement on both obverse and reverse surface sides of the workpiece 23 along an outer peripheral edge portion 23a of the workpiece 23. Consequently, the outer peripheral edge portion 23a of the workpiece 23 is ground by an outer peripheral surface of each of the rotating grinding wheels 27 and 28. In this case, it is preferred that two grinding wheels 27 and 28 for rough grinding and finish grinding be provided as the disk-shaped rotating grinding wheels, and that rough grinding and finish grinding are performed by the same station.