The present invention aims at automatically obtaining a mass spectrum over a wide mass range with a high mass resolution, without the need of the complicated determination of the number of turns or other troublesome computations due to the overtaking of ions on a loop orbit. First, a mass analysis of a target sample is performed under conditions which ensure that the overtaking of ions does not occur, to obtain a mass spectrum with a low mass resolution (S1 and S2). One or more peaks appearing on the mass spectrum are extracted based on predetermined conditions, the mass ranges corresponding to the extracted peaks are determined, and the analysis conditions which ensure that the overtaking of ions does not occur are determined for each of the mass ranges (S3 and S4). Then, in accordance with the analysis conditions, ions within a restricted mass range are selected and ejected from the ion trap to be made to fly along the loop orbit, and mass spectra with a high mass resolution are obtained (S5 and S6). The mass spectrum with a low mass spectrum and the mass spectra with a high mass resolution are eventually combined to create a mass spectrum over a wide mass range (S8).