The invention relates to a draw-in mechanism for an extractible molded insulated case circuit breaker, equipped with main and auxiliary circuits with fixed and movable connectors. The fixed connectors are arranged on the upper horizontal wall of the case, and the interacting movable connectors plug into the fixed connectors when the circuit breaker is immobile. The reversible mechanism movement transmission system comprises a first mechanical link with the movable connectors drive device, and a second mechanical link with the movable circuit breaker support, the assembly being arranged so that the first mechanical link is active when the second mechanical link is broken, and vice-versa. The racking mechanism comprises an operating device with a handle, and a movable mechanical support having a pair of symmetrical rails sliding in slide plates of the chassis, and a rail locking system in the drawn-in and drawn-out positions.