PURPOSE: To convert the kinetic energy of a driven shaft into the potential energy so as to obtain a buffer action, by stopping a member, which is provided in a freely rotatable manner to a driven shaft, and giving displacement to an elastic body, which is placed between this member and the other member that is integrated into one body with the driven shaft.

CONSTITUTION: When printing operation of a copying machine or the like is started, a clutch 30 is turned on, and a gear 28 is coupled with a shaft 26. Thus, the driving force from a gear 22 is transferred to a driven shaft 25 via a gear train, and a drum 21 rotates counterclockwise, thereby moving a scanning mirror in the R-direction. At this time, by turning the clutch off and turning a brake 32 on, the second member 36 of a shock absorber 31 is stopped, while the first member 35 rotates counterclockwise owing to the inertia force, thereby giving diplacement to compression springs 33 and 34. As a result, the displacement of the compression springs 33 and 34 converts the kinetic energy of the scanning mirror into the potential energy, thereby stopping the scanning mirror. As a consequence, the shock of the scanning mirror at the time of, for example, stoppage can be absorbed.