An object of the invention is to automatically remove noise out of an input spectrum data while rounding in spectral shape is being suppressed. The spectrum data correction system wherein a noise quantity is detected on the basis of a difference in value between an extremal point of measurement data-blocks making up input spectrum data, and a mean value of measurement data-blocks in the vicinity of the extremal point, and a count of moving-average points of measurement data-blocks subjected to moving average processing is controlled according to the noise quantity, the spectrum data correction system comprises means for using an optical power, detected by a photo-detector of an optical spectrum analyzer, as the measurement data-block, thereby controlling the count of the moving-average points of the measurement data-blocks according to magnitude of a signal level of the measurement data-block.