A mass spectrometer which sequentially introduces sample components which are temporally separated by a column of a chromatograph into an ionization unit and performs mass analysis, comprising: a) MS analysis performing means (30, 31, 46) for repeatedly performing MS analysis on ions generated in the ionization unit; b) chromatogram creation means for creating a chromatogram that shows changes over time in an ion intensity within a predetermined mass range ΔM based on a result of the MS analysis; c) timing determination means for determining a timing to perform MS/MS analysis based on a signal intensity in the chromatogram; and d) MS/MS analysis performing means (30, 31, 46) for performing MS/MS analysis in which ions belonging to the mass range (ΔM) among ions generated in the ionization unit are adopted as precursor ions, in accordance with the timing to perform MS/MS analysis that is determined by the timing determination means; wherein: the timing determination means is configured so that each time a signal intensity in the chromatogram reaches a predetermined upper limit after exceeding a predetermined lower limit, the timing determination means determines, as the timing to perform MS/MS analysis, the point in time at which the signal intensity in the chromatogram reaches the predetermined upper limit after exceeding the predetermined lower limit; the timing determination means is configured so that if a signal intensity in the chromatogram arrives at a top of a peak, after exceeding the predetermined lower limit, without reaching the upper limit, the timing determination means determines, as the timing to perform MS/MS analysis, the point in time at which, after exceeding the predetermined lower limit, the signal intensity in the chromatogram arrives at a top of a peak without reaching the predetermined upper limit; and the predetermined upper limit corresponds to an amount of precursor ions for MS/MS analysis above which the mass separation performance declines due to the space-charge effect. a) MS analysis performing means (30, 31, 46) for repeatedly performing MS analysis on ions generated in the ionization unit; b) chromatogram creation means for creating a chromatogram that shows changes over time in an ion intensity within a predetermined mass range ΔM based on a result of the MS analysis; c) timing determination means for determining a timing to perform MS/MS analysis based on a signal intensity in the chromatogram; and d) MS/MS analysis performing means (30, 31, 46) for performing MS/MS analysis in which ions belonging to the mass range (ΔM) among ions generated in the ionization unit are adopted as precursor ions, in accordance with the timing to perform MS/MS analysis that is determined by the timing determination means; wherein: the timing determination means is configured so that each time a signal intensity in the chromatogram reaches a predetermined upper limit after exceeding a predetermined lower limit, the timing determination means determines, as the timing to perform MS/MS analysis, the point in time at which the signal intensity in the chromatogram reaches the predetermined upper limit after exceeding the predetermined lower limit; the timing determination means is configured so that if a signal intensity in the chromatogram arrives at a top of a peak, after exceeding the predetermined lower limit, without reaching the upper limit, the timing determination means determines, as the timing to perform MS/MS analysis, the point in time at which, after exceeding the predetermined lower limit, the signal intensity in the chromatogram arrives at a top of a peak without reaching the predetermined upper limit; and the predetermined upper limit corresponds to an amount of precursor ions for MS/MS analysis above which the mass separation performance declines due to the space-charge effect. the timing determination means is configured so that each time a signal intensity in the chromatogram reaches a predetermined upper limit after exceeding a predetermined lower limit, the timing determination means determines, as the timing to perform MS/MS analysis, the point in time at which the signal intensity in the chromatogram reaches the predetermined upper limit after exceeding the predetermined lower limit; the timing determination means is configured so that if a signal intensity in the chromatogram arrives at a top of a peak, after exceeding the predetermined lower limit, without reaching the upper limit, the timing determination means determines, as the timing to perform MS/MS analysis, the point in time at which, after exceeding the predetermined lower limit, the signal intensity in the chromatogram arrives at a top of a peak without reaching the predetermined upper limit; and the predetermined upper limit corresponds to an amount of precursor ions for MS/MS analysis above which the mass separation performance declines due to the space-charge effect.