To prevent an image quality from being deteriorated by having a support shaft for a major rotor, a first rotor fixed to the support shaft, and a second rotor fixed to the support shaft or the first rotor via an elastic meter and by specifying the relation of the inertia moment of each rotor, torsional rigidity of the support shaft, and the circumferential speed of the major rotor by an equation.

This vibration isolator is provided with a support shaft 12, a flywheel 16, and a dynamic vibration reducer 30 composed of an elastic body 31 and a rotation inertia body 32, and the support shaft is integrally and rotatably fixed to a photosensitive drum. The inertia moment Idd of the rotating inertia body 32, the inertia moment If of the flywheel 16, the inertia moment Idr of the photosensitive drum, the torsional rigidity G of the support shaft 12, and the circumferential speed V of the photosensitive drum satisfy an equation and the frequency 21/2 times of resonance frequency is lower than the the lowest limit of the frequency region conspicuous of pitch unevenness. The driving noise is thus damped, the vibration caused by the speed fluctuation of the photosensitive drum is reduced, the pitch unevenness is suppressed, and the image quality deterioration is prevented.