The present invention relates to a method of producing a polymer in the method for producing a copolymer of olefin and a polar group-containing monomer represented by formula (1): C(R1)2═C(R1)(C(R1)2)nR2  (1) (in the formula, the symbols have the same meanings as described in the description), the method comprising using a complex of a metal in Group 10 of the periodic table as a catalyst; and supplying a catalyst solution separated from a polymer after the polymerization reaction to a polymerization reaction system to recycle and re-use the catalyst. The production method of the present invention can dramatically reduce the catalyst cost.