Abstract: A device for guiding a medical instrument (2) inserted into a natural duct (101) or an artificial duct of a patient in order to bring at least a distal end (1) of the instrument in proximity to an internal organ (100). The device includes an articulated arm (3) with a plurality of degrees of freedom, for moving a proximal end (4) of the instrument, and a controlled blocking mechanism (7) for blocking the degrees of freedom of the articulated arm. The blocking mechanism is designed in such a way that, for at least one of the degrees of freedom, a blockage imposed on the degree of freedom can be released when an outer stress exerted on the instrument (2) exceeds a predetermined threshold.