The present invention relates to a novel iron complex having a cyclic amine compound as a ligand and a method for producing polymers by polymerizing a radical polymerizable monomer in the presence of the iron complex and a radical generator. The problem for the present invention is providing a method capable of producing a polymer or block copolymer having a chemically convertible functional group at the end from a radical polymerizable monomer and providing a method for recovering the iron complex in a solvent with a high recovery rate after the polymerization reaction. This problem is solved by providing a novel iron complex, a method for producing a polymer in the presence of a radical polymerization initiator that uses the iron complex as a polymerization catalyst and a method for simply and easily recovering the iron complex. The present invention can provide an iron complex useful for the method for producing a polymer by polymerizing a radical polymerizable monomer and a method for producing the polymer using that iron complex.