Abstract: An automatic balancing device for counterbalancing an out-of-balance mass includes a plurality of counterbalancing masses, each of which is movable in a circular path about the axis so as to generate a balancing force. The balancing forces combine to produce a resultant balancing force which varies between minimum and maximum values. At a first speed of rotation of the body about the axis, the movement of at least one of the counterbalancing masses is restrained so that a substantially constant, non-zero resultant balancing force is produced, the resultant balancing force being freely movable about the axis. At a second speed of rotation of the body about the axis, the counterbalancing masses are free to adopt a position in which the out-of-balance mass is counterbalanced. The device allows at least partial counterbalancing of the out-of-balance mass at speeds below the critical speed of the system in which it is used.