A locking device for a maintenance machine such as a balancing machine, of a rotating body (5), having a fixed portion comprising a hollow fixed support element (2) borne by the maintenance machine, and a control system (59), and a movable portion comprising a bell-shaped member (12) with flange (13) mounted for rotation coaxial to said hollow support element (2) and designed to support the rotating body (5), and holding or locking means (68) arranged to removably fix the rotating body (5) against said flange (13) of the bell-shaped member (12), driving means suitable for driving, upon control, said movable portion in rotation. The movable portion comprises a sleeve element (9), which is operatively connected with the driving means, mounted for rotation on said fixed support element (2) and has one of its ends extending overhanging beyond said fixed support (2) and coaxially supporting at its head the bell-shaped member (12), thereby delimiting a work chamber (17) with said bell-shaped member (12); a piston element (19) slidably mounted in the work chamber (17) and designed to control said holding means. The fixed portion comprises pressurized fluid supply means (34, 32, 48) suitable for loading, upon control of the control system (59), the work chamber (17) with pressurized fluid, and for moving away from the movable portion before the movable portion is set in rotation by the driving means, and discharge means for discharging, upon control, the work chamber (17) once the rotation of the movable part has terminated.