There are many systems for measuring precise position of stages or probes. Three-dimensional coordinate measuring machine is an example. These machines, however, do not measure orientation of the stage. In recent years, positioning stages using parallel mechanisms have been developed. To obtain the information of their geometrical motions, we have to measure the orientation in addition to position. In this paper, we shall propose an interferometric system for measuring the position and orientation of such a positioning stage. In this system multiple retro-reflectors such as corner cubes are fixed on the moving stage and multiple interferometers are formed with the corner cubes as reflectors. Light beams are incident on the corner cubes from different incident directions. We have two ways to measure the positions of the corner cubes with interferometers. One is "fringe counting method", measuring the moving distance of the corner cubes in several directions directly, and calculating the position and orientation of the stage from the moving distances. The other is "multi-directional coincidence method", utilizing multiple image sensors to detect the interferograms in several directions. From the interferograms, we obtain fractional fringe orders by image processing, and estimate the integer fringe orders, which conform to the fractional orders for all the interferograms. The simulation results in 2-dimension (2-D) showed that an error within 0. 1 tm in translation and 0.01 degree in rotation are achieved in the measuring ranges of several millimeters with the fringe counting method. Simulation for one-dimensional multi-directional coincidence method showed the potentiality ofthe method.