A position measuring apparatus, for use in an assisting apparatus for surgical opertions, includes a position indicating apparatus for indicating a position and a direction of a tool, and three-dimensional position measuring apparatus for measuring a position and a direction of a surgical field and also the position and the direction of the tool. The position indicating apparatus and the three dimensional position measuring apparatus are unified in one body in the relative position thereof, so that a position for assistance of surgical operation is indicated in the form of an intersection line or an intersection point of the laser beams, irrespective of the position of the position measuring apparatus.