A DC electrical circuit breaker includes first and second movable electrical contacts. The circuit breaker includes a magnetic circuit including a magnet and generating a magnetic field able to guide an electrical arc in the direction of a quenching chamber, and having for this purpose curved field lines extending perpendicularly to opposite lateral walls of an electrical arc formation chamber, these field lines converging, in a central region of the arc formation chamber containing the contact zones, toward the quenching chamber while extending parallel to the longitudinal plane.