A surface to be tested and an optical system for projecting an index to an apparent spherical center position of the surface to be tested are moved relative to each other and an eccentric quantity of the surface to be tested is calculated from an movement quantity. A focal distance of an optical system is changed according to an apparent radius of curvature of each surface to be tested, which is calculated in advance. A reflection image on a surface to be tested, which is to be measured, is determined from the apparent radius of curvature of each surface to be tested, which is calculated in advance. Thus, an eccentric quantity of the entire lens system is accurately measured.