Compressed data of mass spectra obtained at respective measurement points and normalization coefficients for XIC normalization or the like are stored in a memory (21). When a normalized imaging graphic at a specific m/z value is to be displayed, a data decompression processor (23) reads the minimally required set of compressed data from the memory (21) and restores the intensity value corresponding to the m/z value at each measurement point. A normalizing calculation processor (29) reads an XIC normalization coefficient corresponding to the m/z value from the memory (21) and corrects the intensity values at each measurement point by multiplying those values by the coefficient. An imaging graphic creation processor (27) assigns a display color to each of the corrected intensity values to create an imaging graphic, and displays the imaging graphic on the screen of a display unit (6). According to this method, even in the case of sequentially displaying imaging graphics while changing the normalization condition, those graphics can be displayed at high speeds if the normalization coefficients are previously calculated and stored.