PURPOSE: To prevent a cage and a balance weight from derailment out of rails due to deformations of the guide-rails by hanging the balance weight having a longer period of vibration than a characteristic period of vibration of a housing and providing sliding pieces and the balance weight with springs and dampers.

CONSTITUTION: A balance weight 15 is provided with a damper 26 and a vibration is damped quickly. If vibrating force pushing a sliding piece 19 by a guide rail 17 was given, a frame 11 will move to right through springs 20, however, due to little variation of a position of gravity center because of the phase difference of the balance weight 15 by 180, the balance weight 15 will be only pivoted in clockwise upon movement of a pin 14 to right and distances between guide rails 16, 17 are somewhat spreaded despite the pushing force between the guide-rail 17 and the sliding piece 19 is not so big. Notwithstanding, because the balance weight is pivoted in clockwise, a sliding piece 18 will be moved to right compensating the amount of the deflections of the springs 20 and the elastic deformation of the rail 17 together with reinforcing members 17AW17C.