To restrain generation of wear or frictional sound in a shaft member over a long time by providing a recess part capable of storing lublicant at the outer circumferential part engaging with the mounting hole of rotary member of the shaft member.

A recessed member 41 capable of storing lublicant OL is formed in a shaft member 22 (23-27). Namely, the circumferential groove 41 is annularly formed at the center of the outer circumferential surface 22a-21a of the shaft member 22-27. The width size w1 thereof is made smaller than the width size w2 of gear 32-37 and the depth D is made e.g. 0.5-1mm. Onto the outer circumferential parts 22a-27a of the shaft member 22-27, lublicant OL is applied. Accordingly, if gears are rotationally driven, no lublicant in the groove 41 comes to the outside. Generation of wear or frictional sound in the shaft members can therefore be restrained.