A remote controlled actuator (5) includes a distal end member (2) fitted to a distal end of a spindle guide section (3) for alteration in attitude, and a tool (1) rotatably supported by the distal end member. The navigation system includes a tool and tool marker relative position storage section (54) for storing the relative position of a processing member of the tool relative to the tool marker, and a relative relation storage section (55) having recorded therein the relative position and attitude of the tool marker relative to a main body marker (7A) for each angle of rotation of the distal end member, and a tool processing member position estimator (56) estimates the position of the processing member of the tool from the attitude and position of the main body marker during the actual procedure and the angle of rotation of the distal end member.