A polymerization initiator kit comprising: a first member including: (c) a transition metal compound; and a second member including: (d) an aromatic amine compound, (e) at least one compound selected from sulfinic acid and a salt thereof and (fa) a peroxyester compound and/or (fb) an alkyl peroxide, the transition metal compound (c) is at least one selected from vanadium acetylacetonate, vanadium naphthenate, vanadyl stearate, vanadium benzoylacetonate, bis(maltolate) oxovanadium, oxobis(1-phenyl-1,3-butanedionate) vanadium, vanadyl acetylacetonate, divanadium tetroxide, vanadyl oxalate, vanadyl sulfate, oxobis(1-phenyl-1,3-butanedionate) vanadium, bis(maltolate) oxovanadium, vanadium oxytriisopropoxide, vanadium pentoxide, sodium metavanadate, ammonium metavanadate, copper acetylacetonate, copper oleate, copper acetate, copper gluconate, copper citrate, copper phthalate, copper naphthenate, copper hydroxide, copper methoxide, copper ethoxide, copper isopropoxide, copper chloride, and copper bromide, the aromatic amine compound (d) and the at least one compound (e) being accommodated together or separately, the alkyl peroxide (fb) is a dialkyl peroxide, the first member and the second member are separated from each other. a first member including: (c) a transition metal compound; and a second member including: (d) an aromatic amine compound, (e) at least one compound selected from sulfinic acid and a salt thereof and (fa) a peroxyester compound and/or (fb) an alkyl peroxide, the transition metal compound (c) is at least one selected from vanadium acetylacetonate, vanadium naphthenate, vanadyl stearate, vanadium benzoylacetonate, bis(maltolate) oxovanadium, oxobis(1-phenyl-1,3-butanedionate) vanadium, vanadyl acetylacetonate, divanadium tetroxide, vanadyl oxalate, vanadyl sulfate, oxobis(1-phenyl-1,3-butanedionate) vanadium, bis(maltolate) oxovanadium, vanadium oxytriisopropoxide, vanadium pentoxide, sodium metavanadate, ammonium metavanadate, copper acetylacetonate, copper oleate, copper acetate, copper gluconate, copper citrate, copper phthalate, copper naphthenate, copper hydroxide, copper methoxide, copper ethoxide, copper isopropoxide, copper chloride, and copper bromide, the aromatic amine compound (d) and the at least one compound (e) being accommodated together or separately, the alkyl peroxide (fb) is a dialkyl peroxide, the first member and the second member are separated from each other. (d) an aromatic amine compound, (e) at least one compound selected from sulfinic acid and a salt thereof and (fa) a peroxyester compound and/or (fb) an alkyl peroxide, the transition metal compound (c) is at least one selected from vanadium acetylacetonate, vanadium naphthenate, vanadyl stearate, vanadium benzoylacetonate, bis(maltolate) oxovanadium, oxobis(1-phenyl-1,3-butanedionate) vanadium, vanadyl acetylacetonate, divanadium tetroxide, vanadyl oxalate, vanadyl sulfate, oxobis(1-phenyl-1,3-butanedionate) vanadium, bis(maltolate) oxovanadium, vanadium oxytriisopropoxide, vanadium pentoxide, sodium metavanadate, ammonium metavanadate, copper acetylacetonate, copper oleate, copper acetate, copper gluconate, copper citrate, copper phthalate, copper naphthenate, copper hydroxide, copper methoxide, copper ethoxide, copper isopropoxide, copper chloride, and copper bromide, the aromatic amine compound (d) and the at least one compound (e) being accommodated together or separately, the alkyl peroxide (fb) is a dialkyl peroxide, the first member and the second member are separated from each other.