PURPOSE: To allow the length measure of a rotary shaft to be shortened without lowering the strength of a scissors gear or harming the facility of fitting/ removing a snap ring at the time of fitting the scissors gear for transmitting power in the backlash eliminated state, to a rotary shaft such as a camshaft through the snap ring.

CONSTITUTION: A completely round annular recessed part 15 for fitting a snap ring 13 to be engaged with a rotary shaft 1 so as to hold a scissors gear 3 in the non-slip-off state is formed at the outer side face of an inner peripheral part in a sub-gear 5. An auxiliary recessed part 17 cutout radially from the annular recessed part 15 so as to allow both ends 13a, 13b of the snap ring 13 to be pushed open by a tool is formed at either one or both of the outer side face of the sub gear 5 and the outer peripheral surface of the rotary shaft 1, partially along the circumferential direction, or the outer periphery of the snap ring 13 is formed into complete roundness.