1. A mass spectrometer comprising: a mass analyzer that performs an MS m analysis (where m is an integer greater than two) to obtain mass analysis data for each of a first compound and a second compound; and a data processor configured to a) create an MS m-1 spectrum based on mass analysis data obtained by an MS m-1 analysis performed for each of first and second components by the mass analyzer; b) calculate, for each of the two MS m-1 spectrums, a mass difference between a mass of each peak among some or all of peaks appearing on the MS m-1 spectrum and a mass of a precursor ion, and for creating an MS m-1 mass-difference spectrum having a peak at each of the calculated mass differences; c) extract a common peak having a same mass in the two MS m-1 mass-difference spectrums relating to the first component and the second component; and d) extract a complementary peak on the MS m-1 spectrum relating to the first component and/or the second component, the complementary peak corresponding to a mass difference between the mass of the precursor ion and the mass of the common peak; and an analysis controller that receives an information of the complementary peak from the data processor; determines a candidate of the precursor ion for an m−1-th stage of a dissociation operation in the MS m analysis based on the information; and controls performance of the MS m analysis by the mass analyzer to perform the MS m analysis on the first component and/or the second component with the determined candidate of the precursor ion designated as a precursor ion for an m−1-th stage of the MS m analysis.