To prevent the occurrence of the unpolished part without repeatedly making reciprocating motion while dislocating a locus of a rotary grinding wheel by forming grooves continuing in the circumferential direction so as to be dislocated from a concentric circle.

A rotary grinding wheel 10 is formed by fixing an abrasive material layer 13 to the surface of a plastic disk-shaped base so that spiral grooves 11 and a large number of radial grooves 12 turning to the outer peripheral part from a central hole 14 are formed in the abrasive material layer 13. A spiral shape is set so that the grooves do not exist at the same radial point separate by 180 degrees from a certain one point of these continuous spiral grooves 11. In the rotary grinding wheel 10, since the circumferential directional grooves 11 are formed in a spiral shape in this way, the spiral grooves 11 do not overlap in the circumferential direction when rotating the rotary grinding wheel 10, so that the abrasive material layer 13 contacts with the whole surface of the work object part to thereby prevent the occurrence of the linear unpolished part.