Disclosed is a graft copolymer produced by the graft copolymerization of a polyalkylene glycol or an alkyl ether thereof and a polyfluoro-1-alkene represented by general formula: CnF2n+1(CH2CF2)a(CF2CF2)bCH=CH2 (wherein n represents an integer of 1 to 6; a represents an integer of 1 to 4; and b represents an integer of 1 to 3). The graft copolymer is an oligomeric compound having a perfluoroalkyl group carrying 6 or less carbon atoms, which is a compound that has been believed to have low bioaccumulation potential. When the graft copolymer is used an active ingredient for a mold release agent, the mold release agent can exhibit an equal level of mold release performance to that of a mold release agent in which an oligomeric compound having a perfluoroalkyl group carrying 8 or more carbon atoms is used as an active ingredient.