A surface position detecting apparatus is arranged to be able to detect a surface position of a detection target surface with high accuracy, while restraining influence of a relative positional deviation between polarization components in a beam totally reflected on an internal reflection surface of a prism member, on detection of the surface position of the detection target surface. At least one of a light projection system and a light reception system is provided with a total reflection prism member (7; 8) having an internal reflection surface (7b, 7c; 8b, 8c) which totally reflects an incident beam. For restraining influence of the relative positional deviation between polarization components of the beam totally reflected on the internal reflection surface of the total reflection prism member, on the detection of the surface position of the detection target surface (Wa), a refractive index of an optical material forming the total reflection prism member and an angle of incidence of the incident beam to the internal reflection surface of the total reflection prism member are set so as to satisfy a predetermined relation.