To simply measure an eccentricity with a high precision by decreasing the influence of disturbance by shake or oscillation of air.

A coherent light 91 emitted from a light source 11 is split into measuring lights 91a (92a) and reference lights 91b (92b), and then the measuring light 91a (92b) are cat's eye reflected on a surface 1a of a test lens, while the reference light are reflected at reflecting means (light transmission structure reflecting means 16, 26) without reaching the test lens 1. Interference fringe are formed by combining the measuring light 91a (92a) cat's eye reflected on the surface 1a of the lens and the reference light 91b (92b) reflected on the reflecting means. The interference fringes are simultaneously formed for at least two points of the specimen. Based on the difference of a plurality of the interference fringes resulted when the lens 1 is rotated around a reference axis (the optical axis L of the lens system), the eccentricity to the reference axis of the lens 1 is determined.