Method of controlling mass spectrometer and mass spectrometer

A mass spectrometer that measures partial pressures of a gas to be measured, comprising:

• an ion source which has a cathode electrode and an anode electrode, and supplies current to the cathode electrode to ionize the molecules of the gas to be measured;
• a filter section that selects ions generated in the ion source by mass-to-charge ratio, and passes them through the filter section;
• a detection section that measures an ion current value of the ions passing through the filter section;
• and
• a control section that controls each of the operations of the ion source, the filter section, and the detection section,
• wherein the control section,
• in a case where a partial pressure of the gas to be measured is measured, supplies cathode current to the cathode electrode such that an emission current between the cathode electrode and the anode electrode becomes constant, and
• in a case where a partial pressure of the gas to be measured is not measured, supplies a constant current with a lower current value than that of the cathode current to the cathode electrode.