Provided is a method for recovering, by pressure swing adsorption, unreacted olefins from a stream of a chemical reaction process in which an olefin is used as a material, the method enables desorption of gas at a relatively high desorption operation pressure, more preferably at a pressure not lower than the atmospheric pressure, and enables reuse of a separation agent. As the separation agent, a metal complex is used, in which pressure P3 at which a local maximum of dA/dP is obtained during adsorption and pressure P4 at which a local maximum of dA/dP is obtained during desorption are located between an adsorption operation pressure P1 and a desorption operation pressure P2, where dA/dP represents a value obtained by differentiating A by P, assuming that an olefin adsorption amount (A) is a function of an adsorption pressure (P), i.e., A=f(P), on an adsorption isotherm indicating the pressure (P) and the adsorption amount (A).