In an eccentricity measuring method according to the present invention, a first position of a light source image formed by reflection at one optical surface is measured (S2), a predetermined second position related to another optical surface is measured (S3), and a relative eccentricity between both optical surfaces is calculated based on the first and second positions (S5). Therefore, the eccentricity measuring method enables measurement of eccentricity by a same measurement optical system regardless of a radius of curvature of an optical surface of an optical element.