PURPOSE: To obviate the necessity of alignment of a grinder and a workpiece by using the cup-shaped grinder whose outer diameter is larger than the max. surface to be worked and whose width is wider than the min. surface to be worked.

CONSTITUTION: When the surface 1 to be worked which has the max. grinding dimension is surface-ground, the surface 1 to be worked and a surface grinder 10 are relatively shifted, in accordance with the center of the surface grinder 10, drawing the locus 10a→10b→10c, the surface 1 to be worked is surface-ground. When the surface to be ground which has the min. dimension is surface-ground by the surface grinder 10 in this state, the grinder width 11 which is broader than the surface 2 to be worked contacts the all surface, so the surface 2 to be ground is uniformly surface-ground, and alignment of the workpiece to the center 12 of the surface grinder 10 is not needed.