In a quadrupole mass spectrometer which measures partial pressure strength according to a gas type in a vacuum system from ion current intensity, a quadrupole mass spectrometer with a total pressure measurement electrode has a total pressure measurement electrode for examining an ion density disposed in a demarcation space which is comprised of a grid electrode and an ion focusing electrode. And, a vacuum system is provided with only the quadrupole mass spectrometer which measures partial pressure strength according to a gas type in the vacuum system from an ion current intensity and does not have an ionization vacuum gauge other than the quadrupole mass spectrometer.