The present invention has a mechanical rotation drive mechanism (50) that drives rotation of at least one rotation pinion sprocket (22; 23) on its axis from among a plurality of pinion sprockets (20). The mechanical rotation drive mechanism (50) drives the rotation of at least one rotation pinion sprocket (22; 23) on its axis in concert with a sprocket movement mechanism (40A) so as to eliminate a phase shift, associated with a radial direction movement of the plurality of pinion sprockets (20) by the sprocket movement mechanism (40A), of the plurality of pinion sprockets (20) with respect to a chain (6).