The gas separation method is executed under a condition in which a partial pressure of a first gas (G1) in a feed gas that contains at least mutually different gases being the first gas (G1) and a second gas (G2) becomes less than or equal to a total pressure of a permeate-side space (S2) of a gas separation membrane (30). The gas separation method includes a step of causing flow of a sweep gas that contains at least a third gas (G3) being a different gas from the first gas (G1) and the second gas (G2) into the permeate-side space (S2) of the gas separation membrane (30) while supplying a feed gas to a feed-side space (S1) of the gas separation membrane (30). The permeation rate of the first gas (G1) in the gas separation membrane (30) is greater than the permeation rate respectively of the second gas (G2) and the third gas (G3).