In processing chromatographic data, collected by performing a measurement for each of the segments which respectively define time ranges, a system determines whether there is any boundary sandwiched between two temporally continuous segments whose measurement modes are the same and which has the same m/z value designated by an operator to be displayed. If such a boundary exists, the measurement mode common to the two neighboring segments across that boundary is identified, and the system determines whether the parameter values corresponding to that measurement mode are the same. If they are the same, the partial chromatograms corresponding to the two segments show a temporal change in the intensity of the same kind of ion. Accordingly, the two neighboring measurement points across the boundary are connected by interpolation to create a chromatogram with no missing portion.