To provide an interferometer in which the miniaturization can be achieved and in which the cost can be reduced, in the interferometer using a low coherence light source.

In the interferometer having the low coherence light source 12 and a reference means 16 for making a part of a light from the light source into a reference light, in which shape information on a surface to be inspected is obtained by irradiating the surface to be inspected of an object 28 to be measured with the light from the light source and by making the measuring light from the surface to be inspected interfere with the reference light, the interferometer is provided with: a polarized wave surface preserving optical fiber 14 for providing two perpendicular linearly polarized light components with an optical path length difference; a polarized wave component extraction means 18 for extracting the common polarized light component from a measuring light flux consisting of the reference light and the measuring light; and an imaging means 20 for imaging an interference fringe generated by the interference between the reference light and the measuring light. The optical path difference between the reference light and the measuring light is canceled by passing the light from the light source or the measuring light flux through the polarized wave surface preserving optical fiber, utilizing one of the two perpendicular linearly polarized light components, as the reference light, and the other, as the measuring light, so that the interference fringe is imaged.