An object of the present invention is to provide a high-accuracy measurement method that, in the measurement of the concentration of
fluorine gas contained in a
halogen fluoride-containing gas using a
mass spectrometer, reduces the amount of measurement errors of the concentration of
fluorine gas that are caused by consumption due to reactions between
metal members and impurities, and
fluorine gas on the gas passage. The present invention includes a method for measuring the concentration of fluorine gas (F2) contained in a
halogen fluoride-containing gas by using an analysis apparatus having a
halogen fluoride-containing
gas supply source, a fluorine-containing
gas supply source, a tube, a capillary, and a
mass spectrometer, the method comprising, before measuring the concentration of fluorine gas, performing
passivation treatment on the tube and the capillary by using a
passivation gas containing a fluorine-containing gas supplied from the fluorine-containing
gas supply source.