Disclosed is a graft copolymer in which a polyalkylene glycol or an alkyl ether thereof is graft-copolymerized with a polyfluoro-1-alkene represented by the general formula: CnF2n+(CH2CF2)a(CF2CF2)bCH═CH2 (wherein n is an integer of 1 to 6, a is an integer of 1 to 4, and b is an integer of 1 to 3). The graft copolymer is an oligomer compound having a perfluoroalkyl group containing 6 or less carbon atoms, which is said to have low bioaccumulation potential, and having, when used as an active ingredient of a mold-releasing agent, mold release performance equivalent to that of a compound having a perfluoroalkyl group containing 8 or more carbon atoms.