1. A spectrometer comprising: accumulation means for accumulating M spectral data sets or time-domain data sets S 1 (d 1 to dN) to SM(d 1 to dN) obtained by repeating the same measurement M times, each of the data sets having N data points; correlation computing means for finding correlations between the sets S 1 (dn) to SM(dn) of data points which are contained in the M spectral data sets or time-domain data sets S 1 (d 1 to dN) to SM(d 1 to dN), each of the sets S 1 (dn) to SM(dn) consisting of data points of the same ordinal number dn, to thereby find a correlation data set C(c 1 to cN) indicating correlation strengths about the data points of the ordinal numbers; and computing means for finding a product of an accumulated or anticipated spectral data set or a time-domain data set Sav(d 1 to dN) having the N data points and obtained from the accumulation means and the correlation data set C(c 1 to cN).