A high- or medium-voltage circuit breaker, in which a movable contact (1) is moved in sliding in order to separate stationary contacts (11, 12) from its sliding surface (2). In accordance with the invention, the stationary contacts (11, 12) have switching portions (9) that separate from the movable contact more or less simultaneously as a result of a setback (19) in the movable contact (1), thereby causing two simultaneous switching arcs to appear (14, 15), which arcs are extinguished much more quickly than a single arc, before the current is transferred to the conventional arcing contacts (5). This disposition enables the stationary contacts (11, 12) and their environment to be less exposed to damage.