Abstract: A method for producing fluorine gas including a fluorination step of obtaining a reaction mixture containing a major fluorinated substance that is a target component generated by fluorination of a raw material compound and by-product hydrogen fluoride, a separation step of separating the reaction mixture to obtain a main product component containing the major fluorinated substance and a by-product component containing the by-product hydrogen fluoride, a purification step of purifying the by-product component to obtain a recovered hydrogen fluoride component in which a concentration of an organic substance is reduced and a concentration of the by-product hydrogen fluoride is increased, an electrolysis step of performing electrolysis using the recovered hydrogen fluoride component as at least a part of an electrolyte to produce fluorine gas, and an introduction step of introducing the fluorine gas obtained in the electrolysis step into a reaction field for fluorination in the fluorination step.