PURPOSE: To obtain a position measuring device for measuring the position of a movable body moving on a plane guide not using a combination of linear stages.

CONSTITUTION: When a movable body 21 moves on a plane guide, three laser lights 28a, 28b, 28c are shifted from fixed points 27a, 27c of the movable body 21. The shift at this time is detected by three split sensors 2a, 2b, 2c which in turn generate signals to three driving circuits 5a, 5b, 5c. As a result, three motors 4a, 4b, 4c are driven to rotate three rotary mirrors 3a, 3b, 3c in a direction to offset the shift of the laser beams 28a, 28b, 28c. Accordingly, the laser beams 28a, 28b, 28c are directed to the fixed points 27a, 27c at all times. At this time, the rotating angles of the angular rotary mirrors 3a, 3b, 3c are detected by three rotary encoders 6a, 6b, 6c, whereby the position and inclination of the fixed point 27 are calculated by a position operating part (a) 7a.