Mass spectrometer

A mass spectrometer comprising:

• a linear ion trap including a plurality of rod electrodes positioned substantially parallel to each other around a central axis, the linear ion trap having a plurality of ion-ejection ports for ejecting ions from an internal space surrounded by the rod electrodes to an outside;
• a plurality of conversion dynodes positioned for the plurality of ion-ejection ports in the linear ion trap, respectively, such that each of the conversion dynodes is configured to emit electrons upon receiving ions ejected through a respective one of the ion-ejection ports;
• a shield plate positioned between the linear ion trap and the plurality of conversion dynodes and having a plurality of ion-passage openings for allowing ions ejected through the plurality of ion-ejection ports of the linear ion trap to pass through;
• a common detector section positioned on a same side as the plurality of conversion dynodes with respect to the shield plate and configured to receive electrons emitted from the plurality of conversion dynodes and produce a detection signal corresponding to an amount of the electrons received from the plurality of conversion dynodes;
• and
• a voltage-applying section comprising circuitry configured to apply, to the shield plate, a voltage which attracts ions ejected through the plurality of ion-ejection ports of the linear ion trap, to apply, to the plurality of conversion dynodes, a voltage equal to or higher than the voltage applied to the shield plate, and to apply, to the common detector section, a voltage higher than the voltage applied to the plurality of conversion dynodes.