A surface position detecting apparatus which detects position information of a predetermined surface in an object, comprising a first optical system which projects light from an oblique direction to the predetermined surface; a second optical system which receive the light from the object; a detecting system which receives the light from the second optical system and which detects the position information of the predetermined surface in a direction intersecting the predetermined surface based on the light; and a phase difference imparting system which is arranged in an optical path of at least one of the first and second optical systems and which imparts a phase difference between different portions from each other of light traveling via a surface other than the predetermined surface in the object, in the light from the second optical system.