If spatial measurement point intervals in imaging mass analysis data of two samples to be compared are different and the degrees of spatial distribution spreading of substances are compared, one of the data is defined as a reference, the measurement point intervals in the other of the data are redefined so as to be equalized to the reference, and a mass spectrum at each virtual measurement point set as a result of the redefinition is obtained through interpolation or extrapolation based on a mass spectrum at an actual measurement points. If the arrays of the m/z values of mass spectra are different for each sample, the m/z value positions of the mass spectrum in one of the data are defined as a reference, and the intensity values corresponding to the reference m/z values are obtained through interpolation or extrapolation for the mass spectrum of the other of the data.