The object of the present invention is to provide a method of producing a polymer wherein radical-polymerizable monomers can be polymerized in a quantitative manner in a relatively short time, and a polymer or a block copolymer having at its termini a functional group that can be chemically converted while the polymer or the block copolymer has a high molecular weight can be produced. Furthermore, the object of the present invention is to provide a method of producing a polymer wherein the polymer is re-precipitated in a general solvent by an easy method, and the used iron complexes are recovered in the solvent, thereby recycling the iron complexes.