A two-dimensional chromatogram creator creates a two-dimensional chromatogram based on data obtained for each of two samples. A chromatogram difference calculator creates a two-dimensional differential chromatogram showing the intensity difference between the two two-dimensional chromatograms. A blob detector detects blobs on each chromatogram. A matching-blob extractor compares the blobs located on the differential chromatogram with those located on each of the two other chromatograms, to extract blobs which can be considered to be located at the same temporal position. If there are two blobs extracted at the same temporal position on the two chromatograms, a normalized value of the intensity difference between the two blobs is calculated, and the line type of the boundary line for indicating the extracted blob on the display is chosen according to that value. Important blobs having significant intensity differences on the two chromatograms being compared can be automatically selected and presented to analysis operators.