A model for locating a peak portion in a chromatogram or similar waveform is trained by machine learning using multiple sets of partial waveforms prepared by dividing each reference waveform having a known peak position. An analysis-target waveform is divided into partial waveforms, and whether or not a partial waveform is a peak portion is determined for each partial waveform by the trained model, to estimate different kinds of regions in the analysis-target waveform, including an overlap-peak region. For an overlap peak within a region estimated to be an overlap-peak region, whether or not that peak is a multimodal peak originating from one component is determined, using at least the height of a peak in the overlap peak, the depth of the trough between two neighboring peaks, or the horizontal width of the portion between the bottom of the trough and the top of one of the neighboring peaks.