The present invention provides a chromatograph/mass spectrometer capable of producing a composite chromatogram from plural chromatogram signals without causing the baseline level to rise or the intensity of the chromatogram peak to decrease. The chromatograph/mass spectrometer includes a chromatograph unit for separating a sample into components in the order of time, a mass spectrometer unit for analyzing the components of the sample, and a signal generator for producing a signal carrying a chromatogram obtained by the analysis. It also includes a chromatogram composer for receiving signals of plural chromatograms simultaneously measured under different conditions, for choosing the largest value of the plural signals for each point in time, and for integrating the chosen values to produce a composite chromatogram.