A remote controlled actuator (5) includes an actuator main body (10), a distal end member (2) fitted to a distal end of a spindle guide section (3) of the actuator main body (10) for alteration in attitude, and a tool (1) rotatably supported by the distal end member (2). The navigation system includes a tool processing member position estimator (55) for estimating the position of a processing member (1a) of the tool (1) from information on the position and attitude of a marker (7A), fitted to the actuator main body (10), that are detected by a marker detecting unit (8), information on the attitude of the distal end member (2) relative to the actuator main body (10), information on the relative position of the distal end member (2) relative to the marker (7A), and information on the shape of the tool (1).
