Disclosed is a method of manufacturing a copolymer of a conjugated diene compound and an olefin other than the conjugated diene compound, where a conjugated diene compound and an olefin other than the conjugated diene compound is copolymerized in the presence of a polymerization catalyst composition containing components: (A) a rare earth element compound or a reactant of the rare earth element compound and a Lewis base; and (B) at least one selected from a group consisting of an ionic compound (B-1) composed of a non-coordinating anion and a cation, an aluminoxane (B-2), and at least one kind of halogen compound (B-3) selected from among a Lewis acid, a complex compound of a metal halide and a Lewis base, and an organic compound containing active halogen (when containing at least one of (B-1) and (B-3), the polymerization catalyst composition further contains component (C): an organometallic compound).