The present invention provides a tandem type mass analysis system capable of carrying out the differential analysis with high efficiency by the tandem type mass analysis. A predetermined number of m/z regions are set up for carrying out the mass analysis with the all ions included therein being dissociated collectively for each m/z region so as to obtain measurement MS2 data. By comparing the measurement MS2 data with reference MS2 data stored in a reference data base, a difference thereof is detected. For the m/z region with a differential component detected, the mass analysis is carried out collectively without dissociation for the all ions included therein so as to obtain measurement MS1 data. By comparing the measurement MS1 data with the reference MS1 data, a difference thereof is detected. From the difference thereof, a parent ion considered to be the differential component factor is presumed for carrying out the mass analysis with the same being dissociated.