To provide a method that can easily inspect a striae without using a liquid with an index of refraction close to that of a member, in which the conventional striae inspection immerses the member to inspect with transmission light without the influence of the curvature of the surface of the member.

Parallel optical flux from a Zygo interferometer is divided into with a half-mirror, and one of the flux is entered into an afocal system formed with a collimator and reference lens, and reflected with a total reflection mirror at the back of the system to be returned to a same optical path. The other flux is entered into an afocal system formed with a collimator and a lens to be inspected, and reflected with a total reflection mirror to be interfered with the flux of the reference lens. In these processes, the phase state of an interference fringe is observed with using double-fetching and the repair functions of the Zygo interferometer.