When a user designates a region of interest for a plurality of groups targeted for difference analysis in a microscopic observation image of a sample, an m/z candidate search unit searches for candidates for m/z presumed to differ, based on collected mass spectral data. An intensity histogram creation unit processing unit creates and displays a graph showing a frequency distribution of peak intensities at measurement points included in the ROI of the groups for each of the m/z candidates. If this graph exhibits multimodality, the data distribution is not suitable for a statistical hypothesis test. An intensity range determination unit limits an intensity range in accordance with a user's instruction. Then, ROI correction unit corrects the ROI so as to include only measurement points with peak intensities within the limited intensity range. A test processing unit performs a statistical hypothesis test using the data corresponding to the corrected ROI.