In a time-of-flight spectrum obtained when the overtaking of ions of different kinds has occurred, mass-to-charge ratios M1, M2, and M3 are computed with a predetermined conversion formula by using a plurality of assumed numbers of turns for one peak. Then, the flight times Tf1, Tf2, and Tf3 for an overtakingless measurement are computed by using an inverse conversion formula. If peaks respectively corresponding to the flight times Tf1, Tf2, and Tf3 for an overtakingless measurement exist on an overtakingless time-of-flight spectrum, their intensities i1, i2, and i3 are obtained. Then, the intensity Ia of the original peak is distributed to the mass-to-charge ratios M1, M2, and M3 in accordance with the intensity ratio. The same intensity distribution processing is performed for all or selected plural peaks. The intensities assigned to the same mass-to-charge ratio are integrated. A mass spectrum is created for each of a plurality of overtaking time-of-flight spectra obtained by changing the timing of deviation of ions from a loop orbit, and the plurality of mass spectra are displayed in a window of a display unit so that they can be compared. Thereby, the probability of missing an ion due to the ion deviation timing can be reduced.