To properly restrain loading from being fluctuated as the whole of a rolling operation, and reduce the jumping operation of each roller when the fillet part of a crank shaft is formed by applying the rolling operation of a multi-point roller having a plurality of rollers arranged at equal intervals every specified angle, to each groove cutting portion cut into a polygon shaped groove having the specified number of crests every specified angle, using a mirror processing machine.

The processing condition of a mirror processing machine is so set in such a way that the number (n) of crests shall be other than the multiple of the number of rollers with respect to the number (three) of the rollers. By this constitution, when one roller comes in the crest or trough portion of a groove cutting portion, the other two rollers come in to a portion other than the crest or trough of a groove cutting portion. Besides, the three rollers are shifted from the crest portion of the groove cutting portion to its trough portion by different timing respectively.