The invention relates to a device for assisting in positioning a medical device (2) inserted in a natural way (100) or an artificial tract of a patient relative to an inner member (P) of a patient, the device comprising a support (1) for insertion at least partially into the patient's body and which carries the medical instrument; displacement means of the support, said moving means comprising an articulated arm (9) which comprises a plurality of degrees of freedom for moving a proximal end (la) of the support; image acquisition means of the inner member for positioning the medical device relatively to the inner member, the image acquisition means including a probe (5) carried by the support so that the instrument medical and sensor are rigidly connected and a control member (10) displacement means which is connected to the image acquisition means and which includes image analyzing means (11) for generating control commands to destination of the articulated arm in order to control at least one movement of the medical instrument relative to the inner member. The invention also relates to a method for controlling such a device.