To solve the problem wherein, in the case where a plurality of target ions for the base of quantitative calculation are set when performing SIM measurement, a monitoring time per ion of one kind is shortened, and detection sensitivity is reduced.

Only target ions T1, T2, T3 are detected in the SIM measurement at the point of GC analysis starting time (a), and resultantly a mass chromatogram is produced in real time. When a peak of the target ion T1 is started to appear, detection of identification ions D11, D12, D13 for identifying the target ion T1 is started (b), and it is confirmed whether the target ion T1 is derived from an object compound or not by utilizing a detection result of the identification ions. Since only the identification ions to the target ion whose peak is appearing are detected, the number of ion kinds to be detected during one MS period can be reduced, and the monitoring time td of the target ion can be secured long.