Abstract: An operating mechanism having a guiding circular plate (9b) provided at a side surface of a gear wheel (9), an annular groove (15d) formed in a pinion (15) into which the guiding circular plate (9b) is fitted whereby the relative position in axial direction between the pinion (15) and the gear wheel (9) does not change even if there is an axial displacement of the gear wheel (9) or the pinion (15) due to a play. Accordingly, there is obtainable a stable angular position of the gear wheel (9) in the disconnection between the pinion (15) and a clutch driving element (16), via a cam constituted by a end-face cam (a projection) (9a) provided at a side surface of the gear wheel (9) and the clutch driving element (16).