PURPOSE: To prevent an abnormal sound from generating at the time of rotating a gear by providing a means which moves a frame supporting a 2nd gear to and away from a frame supporting a 1st gear so that a 1st and a 2nd gear are engaged with each other or disengaged from each other.

CONSTITUTION: A gear 6 is supported by a lower holder 4 (1st frame) and a gear 2 is supported rotatably by a lower holder 4. A gear 1, on the other hand, is supported rotatably on a frame 3 (2nd frame) by a support shaft 5. Screw holes 9 and 8 are formed in the lower holder 4 and frame 3. Then the backlash between the gears 6 and 2, and 1 is adjusted according to the clamping extent of a blush head screw 10. Consequently, fine adjustments can be made, device by device, observing the generation state of an abnormal sound and the rotation state of the gears and the abnormal sound in eccentric cam rotation is prevented from being generated.