To provide a quick automization method for eliminating unnecessary peak from an interferogram before analysis.

This method of processing interferometer data on a sample having a repeated reflecting surface comprises a step of specifying a receiving range of a first set to a concerned peak in the interferogram, a step of determining which peak of the interferogram is within the receiving range, a step of discriminating which peak of the receiving range shows repeated reflection and eliminating a peak showing the repeated reflection from the interferometer data, a step of discriminating the receiving range not containing a peak, and a step of using another peak in the interferogram to calculate a place of a peak within the receiving range not containing a peak.