The present invention relates to a circuit-breaking device for low-voltage systems with a control mechanism that has improved characteristics of compact size and reliability. The circuit-breaking device according to the invention comprises an outer housing containing, for each pole, at least one fixed contact and at least one moving contact suitable for being mutually coupled and uncoupled. The device also comprises a control mechanism comprising a supporting frame that supports a kinematic chain operatively connected to the moving contact so as to enable the latter to be coupled to or uncoupled from the fixed contact. The supporting frame comprises a pair of sides connected by means of a first transverse connecting portion and by further connection means that define a further transverse connecting portion in a different position from that of the first transverse connecting portion.