To form an anti-rolling device that can render a retaining area, i.e., a retaining angle small at which a gimbal is retained, while a frictional force can be set for giving sufficient damping effects to the main system.

There is provided a rotating plate 70 including a friction board 71 on the rotating shaft 13 of a gimbal. Also, a stationary friction board 60 fixed on a main system or the like is provided, and a switch 61 is put on the stationary friction board 60 for detecting a rotational angle of the gimbal. A controller 63 operates to control the magnetic force of a coil 62 through the agency of detecting signals of the switch 61 so as to vary frictional force between the friction board 71 and the stationary friction board 60. As such, frictional force can be set in accordance with a rotational angle of the gimbal.