Patent ID: 8891090

Claim:
A light-interference measuring apparatus, comprising: a light source to output a broad band light; an objective lens section to branch an optical path of the broad band light output from the light source into a reference optical path including a reference mirror and a measuring optical path including a measuring object, and to output a superposed wave of a reference light reflected by the reference mirror and an object light reflected by the measuring object; and an imaging section to form an interference image data of the superposed wave output from the objective lens section, the objective lens section includes: a phase difference control member configured to shift a phase of the object light by 180° when the object light transmits through the phase difference control member twice so as to generate destructive interference fringes at a position at which an optical path difference between the reference optical path and the measuring optical path is zero, a minimum luminance position detecting section configured to detect a minimum luminance position of the destructive interference fringes based on the interference image data formed by the imaging section, wherein the object light passing through the measuring optical path transmits through the phase difference control member twice and thereby the phase of the transmitted light is shifted by 180°, and the reference light passing through the reference optical path is reflected from the phase difference control member so as to retain a phase of the light.