When setting analysis conditions, an analysis operator sets, on a dwell-time calculation/loop-time listing window, the target value of a loop time corresponding to the measurement-time interval to repeat an analysis for one ion, and clicks a dwell time calculation button. Then, a dwell time calculator computes the dwell time for each event, based on the target value of the loop time, the arrangement of events set at that point in time, the number of target ion species set in each event, and other conditional factors. The calculated result is displayed in a dwell time calculation result display field in a listing table. The largest and smallest values of the dwell time are displayed in the largest/smallest dwell time display field. The analysis operator checks this display and changes the target value of the loop time and/or the measurement time of the event so as to achieve an appropriate dwell time.