Abstract: Loopback rolls which can transfer and guide a polishing tape (T) along a perimeter of a pressure contact roll (R) is provided, the pressure contact roll having a tapered peripheral edge having a top edge and a pair of slant edge faces formed on a periphery of the pressure contact roll, by which the polishing tape can be bent into a substantially V-shape in cross section, and a switchable pressure contact mechanism is switchably provided which pressure contacts each of bent portions of the polishing tape, which is bent into the substantially V-shape in cross section by the tapered peripheral edge, to one tooth face (B1) or the other tooth face of a worm.

Abstract: Loopback rolls which can transfer and guide a polishing tape (T) in a tangential direction of a pressure contact roll (R) is provided, a top edge face (RG1) and a tapered peripheral edge (RG) having a pair of slant edge faces (RG2) are formed on a periphery of the pressure contact roll, by both of which the polishing tape can be bent into a substantially V-shape in cross section, and a switchable pressure contact mechanism (7) is switchably provided which pressure contacts each of bent portions (T) of the polishing tape, which is bent into the substantially V-shape in cross section by the tapered peripheral edge to one tooth face (B1) or the other tooth face of a bottom land (B) of a worm (W).