To provide a device to deliver a calibrant gas to the ionizing area of a mass spectrometer at a selected flow rate, and provide a delivery device using a calibrated limiter and a valve continuously pressurized.

This gas delivery device 11 to deliver the calibrant gas to the ionizing chamber of the mass spectrometer 13 evacuated by a vacuum pump has a calibrant gas source, a first valve to selectively connect the calibrant gas source either to the ionizing chamber of the mass spectrometer or to the vacuum pump, a first flow limiter 17 and a second flow limiter 18 to selectively deliver the calibrant gas at a first flow rate and a second flow rate, and a valve to selectively deliver the gas to an ionizing area at the first or second flow rate by selectively connecting the first flow limiter or the second flow limiter to the first valve.