A step (1) of heating a fluoronickel compound to release a fluorine gas, a step (2) of allowing a fluorine gas to be occluded into a fluorinated compound, and a step (3) of heating the fluoronickel compound and reducing an inner pressure are conducted in a container, respectively, at least once, and thereafter a high-purity fluorine gas is obtained in the step (1). Also, a step (5) of heating a fluoronickel compound and reducing an inner pressure and a step (6) of allowing a fluorine gas reduced in a hydrogen fluoride content to be occluded into the fluoronickel compound are conducted in a container having a fluorinated layer formed on its surface, respectively, at least once, the step (5) is further conducted, and thereafter a fluorine gas containing impurity gases is contacted with the fluoronickel compound to fix and remove the fluorine gas, and the impurities are analyzed by gas chromatography.