DETECTING APPARATUS FOR ROTATION OF X-Y STAGE

PROBLEM TO BE SOLVED: To obtain a detecting apparatus whose detecting accuracy is enhanced by a method wherein the size of a plane mirror used to optically detect the rotation of an X-Y stage is reduced. SOLUTION: A first plane mirror 33 which reflects a light beam incident from the Y-direction is arranged on a Y-table 13 which is moved in the Y- direction. A second plane mirror 34 which reflects a light beam incident on the X-direction is arranged on an X-table which is moved in the X-direction. A light beam which is radiated from a light source 18 is made incident on the first plane mirror 33 via a first polarization beam splitter 20 and a second polarization beam splitter 31. The light beam which is reflected here is made incident on the second plane mirror 34 via the second polarization beam splitter 31. The light beam which is reflected here is made incident on the first beam splitter 20 via the second beam splitter 31 and the first plane mirror 33. The light beam which is reflected here is made incident on an optical position detector 24.