A device for controlling a circuit-breaker intended for opening and closing this electric power cut-off device comprising a mobile contact, this control device comprising a motor with a rotary output shaft and being connected to power supply means and actuating means transforming the output displacement of the motor into a displacement of the contact, this device also comprising a mechanical spring arrangement involved in opening and closing the contact. The actuation means include a set of jointed elements providing the connection of the rotary shaft and of the ring, and, in the closed position of the contact, the set of jointed elements is near a dead centre position, a so-called open dead centre, the opening spring being only able to drive it towards the open position upon moving past this dead centre during opening.