Abstract: The invention relates to surgical instruments for use in neurosurgery, anaesthesiology and other fields of medicine. The device provides the automatic atraumatic installation of medical instruments, such as a catheter, an electrode, to mention just few, into various spaces and hollow organs of a human body for a specified depth: the epidural or subdural space of the spinal cord, vessels, a joint cavity etc. Sequentially after passage of dense tissues by a needle (2) and entry of the needle's (2) end into the initial parts of the epidural space, a spring (10) operates and a second tube (9) travels inside a first tube (8). An arresting device (12) is moved together with the second tube (9) and a medical instrument (4). At the end of movement, the arresting device (12) interacts with an end face (14) of a slot (13). The result: the assured automatic movement of the medical instrument for a regulated depth (FIG. I).