An exposure apparatus for exposing a substrate by projecting a pattern image with a projection optical system, the exposure apparatus comprising: a substrate holder for holding the substrate; a position detecting apparatus configured to detect a correction amount for positioning a surface of the substrate relative to the projection optical system; and a driving apparatus (22, 23) for driving the substrate holder on the basis of the correction amount, the position detecting apparatus comprising: a light projecting system for projecting a light beam onto the surface of the substrate on the substrate holder via a first reflecting surface (7b, 7c) from a diagonal direction relative to the surface of the substrate; a light receiving system for receiving the light beam arriving from the surface of the substrate by being reflected at the surface of the substrate, the light receiving system comprising a second reflecting surface (8b, 8c) to reflect the light beam; and a controlling system (17, 18) for deriving the correction amount on the basis of an output of the light receiving system, characterized by: a polarization converting member for converting polarization directions of polarization components of the light beam arriving from the first reflecting surface so that a P-polarized component with respect to the first reflecting surface is converted into an S-polarized component with respect to the second reflecting surface and an S-polarized component with respect to the first reflecting surface is converted into a P-polarized component with respect to the second reflecting surface, the polarization converting member being arranged in an optical path of the light beam from the first reflecting surface to the second reflecting surface. a substrate holder for holding the substrate; a position detecting apparatus configured to detect a correction amount for positioning a surface of the substrate relative to the projection optical system; and a driving apparatus (22, 23) for driving the substrate holder on the basis of the correction amount, the position detecting apparatus comprising: a light projecting system for projecting a light beam onto the surface of the substrate on the substrate holder via a first reflecting surface (7b, 7c) from a diagonal direction relative to the surface of the substrate; a light receiving system for receiving the light beam arriving from the surface of the substrate by being reflected at the surface of the substrate, the light receiving system comprising a second reflecting surface (8b, 8c) to reflect the light beam; and a controlling system (17, 18) for deriving the correction amount on the basis of an output of the light receiving system, a light projecting system for projecting a light beam onto the surface of the substrate on the substrate holder via a first reflecting surface (7b, 7c) from a diagonal direction relative to the surface of the substrate; a light receiving system for receiving the light beam arriving from the surface of the substrate by being reflected at the surface of the substrate, the light receiving system comprising a second reflecting surface (8b, 8c) to reflect the light beam; and a controlling system (17, 18) for deriving the correction amount on the basis of an output of the light receiving system, characterized by: a polarization converting member for converting polarization directions of polarization components of the light beam arriving from the first reflecting surface so that a P-polarized component with respect to the first reflecting surface is converted into an S-polarized component with respect to the second reflecting surface and an S-polarized component with respect to the first reflecting surface is converted into a P-polarized component with respect to the second reflecting surface, the polarization converting member being arranged in an optical path of the light beam from the first reflecting surface to the second reflecting surface. a polarization converting member for converting polarization directions of polarization components of the light beam arriving from the first reflecting surface so that a P-polarized component with respect to the first reflecting surface is converted into an S-polarized component with respect to the second reflecting surface and an S-polarized component with respect to the first reflecting surface is converted into a P-polarized component with respect to the second reflecting surface, the polarization converting member being arranged in an optical path of the light beam from the first reflecting surface to the second reflecting surface.