Even when only mass spectra wherein the reproducibility of peak intensities is low are obtained in a mass spectrometry apparatus using, for example, a MALDI ion source, the correction of shifts in retention time using TICs for a plurality of specimens is performed with good precision. For each mass spectrum, variable scaling is executed which combines such first scaling as to equalize the extent of variations in signal intensity values in one mass spectrum, among different mass spectra, and second scaling for performing weighting according to relative variations in signal intensity values for each mass spectrum (S3). The signal intensity values after the scaling are added to obtain a total signal intensity value for one measurement time point (S4). From a plurality of total signal intensity values thus obtained, a TIC is created (S6). Using these TICs, RT alignment is executed (S8). Thus, the similarity in TIC waveforms increases, and RT alignment can be suitably performed.