Abstract: A device for non-contacting measurement of the orientation in space of a movable measuring object, such as the end-effector of a robot, uses a retro-reflector having three mutually orthogonal reflecting surfaces. This retro-reflector is rigidly attached to the measuring object. Reference marks are provided on the retro-reflector. A laser emits a laser beam. A beam expander optical system in the path of the laser beam provides a collimated light beam of larger diameter than that of said laser beam. The light beam passes through a stationary section, where the path of rays of the light beam is stationary, to a beam directing device. The beam directing device directs collimated light beam onto the retro-reflector. The light beam is returned by the retro-reflector substantially into itself. The beam directing means has movable reflecting surfaces for tracking, with said light beam, the movable measuring object.