Provided is a method for producing a fluorine-containing organic compound. The method can immediately detect the occurrence of a side reaction in direct fluorination reaction using fluorine gas and can give a highly pure fluorine-containing organic compound at a high yield. A raw material liquid (1) containing a raw material organic compound having a hydrogen atom and two or more carbon atoms is reacted with fluorine gas in a reaction container (11) to replace the hydrogen atom of the raw material organic compound with a fluorine atom to give a fluorine-containing organic compound. In the reaction, tetrafluoromethane contained in a gas phase (2) in the reaction container (11) is continuously measured, and the amount of the fluorine gas supplied to the reaction container (11) is controlled depending on the measured value of the tetrafluoromethane.