Patent ID: 8248593

Claim:
An interference measuring device comprising: a light source for outputting light; an interference optical system for splitting the light outputted from the light source into two, so as to output first and second branched beams, inputting a first reflected beam occurring when the first branched beam is reflected by a first subject and a second reflected beam occurring when the second branched beam is reflected by a second subject, and causing the first and second reflected beams to interfere with each other, so as to output thus interfering light; an imaging optical system for focusing the interfering light outputted from the interference optical system; an imaging unit for capturing an interference pattern of the interfering light focused by the imaging optical system; optical path length difference detecting means for detecting an optical path length difference between an optical path length from the light source to the imaging unit by way of the first subject and an optical path length from the light source to the imaging unit by way of the second subject; optical path length difference adjusting means for adjusting the optical path length difference; and a control unit for controlling an optical path length difference adjusting operation by the optical path length difference adjusting means such that the optical path length difference becomes a plurality of target values in sequence according to a result of the optical path length difference detection by the optical path length difference detecting means; wherein the optical path length difference adjusting means includes first moving means for moving the first subject and second moving means for moving the second subject and adjusts the optical path length difference by a moving operation by the first or second moving means; wherein the first moving means has an operating range narrower than that of the second moving means and a positional accuracy higher than that of the second moving means; wherein the second moving means moves the second subject while keeping an optical system between the interference optical system and the second subject; wherein the control unit causes the second moving means to perform the moving operation continuously or intermittently such that an amount of movement by the first moving means falls within a predetermined range within the operating range at each of the plurality of target values, and subjects the moving operation by the first moving means to a feedback control such that the optical path length difference becomes each target value upon the moving operation by the second moving means as well according to the result of the optical path length difference detection by the optical path length difference detecting means.