DC electrical circuit breaker, comprising: - first and second input and output terminals for a direct electric current, - first (21; 21') and second electrical contacts which are connected to the first and second terminals, respectively, and are selectively displaceable relative to one another along a longitudinal plane of the circuit breaker, between: • a closed position, in which respective contact zones (22, 30) of the first and second electrical contacts are in contact with one another in order to allow the direct electric current to flow between the first and second electrical contacts, and • an open position, in which the contact zones are remote from one another, - a formation chamber for an electric arc, in which the contact zones (22, 30) are positioned; - a breaking chamber for an electric arc; - a magnetic circuit which includes a magnet (50, 50') and generates a magnetic field which is capable of guiding, in the direction towards the breaking chamber, an electric arc that forms between the contact zones (22, 30) in the open position, the magnetic field generated by the magnetic circuit having for that purpose curved field lines which extend substantially perpendicularly to opposing side walls (31, 32) of the electric arc formation chamber, the side walls being arranged on either side of the contact zones (22, 30) substantially parallel to the longitudinal plane, the field lines converging, at the level of a central region of the arc formation chamber containing the contact zones (22, 30), towards the breaking chamber while extending parallel to the longitudinal plane, the magnetic circuit further comprises a magnetic core (23, 23') made of ferromagnetic material and which extends at least in part along the first electrical contact, the circuit breaker being characterised in that the first electrical contact has the form of a bar made of an electrically conducting material and comprising two superposed straight portions which extend parallel to one another and are connected together by a curved "U"-shaped portion, the contact zone of the first electrical contact being formed on one of the straight portions, in that the magnetic core has the form of a rectilinear bar which extends between the two superposed straight portions of the first electrical contact, parallel to the two straight portions, and in that the magnet (50, 50') is positioned at one of the ends of the magnetic core (23, 23') and is capable of generating a magnetic field greater than or equal to 0.5 tesla or, preferably, greater than or equal to 1 tesla. - first and second input and output terminals for a direct electric current, - first (21; 21') and second electrical contacts which are connected to the first and second terminals, respectively, and are selectively displaceable relative to one another along a longitudinal plane of the circuit breaker, between: • a closed position, in which respective contact zones (22, 30) of the first and second electrical contacts are in contact with one another in order to allow the direct electric current to flow between the first and second electrical contacts, and • an open position, in which the contact zones are remote from one another, • a closed position, in which respective contact zones (22, 30) of the first and second electrical contacts are in contact with one another in order to allow the direct electric current to flow between the first and second electrical contacts, and • an open position, in which the contact zones are remote from one another, - a formation chamber for an electric arc, in which the contact zones (22, 30) are positioned; - a breaking chamber for an electric arc; - a magnetic circuit which includes a magnet (50, 50') and generates a magnetic field which is capable of guiding, in the direction towards the breaking chamber, an electric arc that forms between the contact zones (22, 30) in the open position, the magnetic field generated by the magnetic circuit having for that purpose curved field lines which extend substantially perpendicularly to opposing side walls (31, 32) of the electric arc formation chamber, the side walls being arranged on either side of the contact zones (22, 30) substantially parallel to the longitudinal plane, the field lines converging, at the level of a central region of the arc formation chamber containing the contact zones (22, 30), towards the breaking chamber while extending parallel to the longitudinal plane,