A sample group forming section 24 classifies samples derived from microorganisms into groups according to empirical information showing the species or strain of each sample. A differential analysis section 27 performs a differential analysis using a peak matrix created based on the result of the grouping. An operator enters group rearrangement conditions concerning the drug resistance of microorganisms. Under the entered conditions, a sample group rearranging/rearrangement-cancelling section 25 rearranges the already formed groups by selecting or merging groups using another kind of previously registered empirical information which shows the drug resistance of each group. The differential analysis section 27 performs a differential analysis using a peak matrix newly created based on the result of the rearrangement of the groups. Thus, differential analysis results concerning the resistance to different drugs can be sequentially acquired as the group rearrangement condition is successively changed.