A polymerizable composition comprising an organoborane, wherein the organoborane is organoboranes in which the boron atom has an empty p orbital or electrophilic properties, and wherein the organoborane is a compound represented by BR 3, wherein B is a boron atom and R independently at each occurrence is a C 1-20 alkyl group, a C 6-20 aryl group, a C 3-20 saturated or unsaturated alicyclic group, a C 1-20 alkoxy group, or a C 2-20 alkyl (amino) alkoxy group (N(R 1) m n -R 2 O-, wherein R 1 is an alkyl group, R 2 is an alkylene group, m is 1 or 2, and n is 1 or 0, an acidic group-free polymerizable monomer having at least one ethylenically unsaturated group capable of undergoing radical polymerization, and a stabilizer for the organoborane, wherein the stabilizer includes a stabilizer, and wherein the stabilizer is at least one selected from: (C2a) a compound represented by formula R A -CO-R D -CO-CHR B R C, wherein R A is a hydrocarbon group, R B and R C are each independently a hydrogen atom or a hydrocarbon group, and R D is a direct bond, a methylene group or a 1,2-ethylene group, (C2b) an ascorbic acid, calciferol, α-tocopherol or quercetin, (C2c) a carotene, and (C2d) at least one class of compounds selected from reducing compounds and hydrotalcite-like compounds, wherein the reducing compound is dibutyltin dilaurate, and the hydrotalcite-like compound is magnesium aluminometasilicate Al 2 O 3 ·MgO·1.7SiO 2 · n H 2 O. an organoborane, wherein the organoborane is organoboranes in which the boron atom has an empty p orbital or electrophilic properties, and wherein the organoborane is a compound represented by BR 3, wherein B is a boron atom and R independently at each occurrence is a C 1-20 alkyl group, a C 6-20 aryl group, a C 3-20 saturated or unsaturated alicyclic group, a C 1-20 alkoxy group, or a C 2-20 alkyl (amino) alkoxy group (N(R 1) m n -R 2 O-, wherein R 1 is an alkyl group, R 2 is an alkylene group, m is 1 or 2, and n is 1 or 0, wherein the organoborane is organoboranes in which the boron atom has an empty p orbital or electrophilic properties, and wherein the organoborane is a compound represented by BR 3, wherein B is a boron atom and R independently at each occurrence is a C 1-20 alkyl group, a C 6-20 aryl group, a C 3-20 saturated or unsaturated alicyclic group, a C 1-20 alkoxy group, or a C 2-20 alkyl (amino) alkoxy group (N(R 1) m n -R 2 O-, wherein R 1 is an alkyl group, R 2 is an alkylene group, m is 1 or 2, and n is 1 or 0, an acidic group-free polymerizable monomer having at least one ethylenically unsaturated group capable of undergoing radical polymerization, and a stabilizer for the organoborane, wherein the stabilizer includes a stabilizer, and wherein the stabilizer is at least one selected from: (C2a) a compound represented by formula R A -CO-R D -CO-CHR B R C, wherein R A is a hydrocarbon group, R B and R C are each independently a hydrogen atom or a hydrocarbon group, and R D is a direct bond, a methylene group or a 1,2-ethylene group, (C2b) an ascorbic acid, calciferol, α-tocopherol or quercetin, (C2c) a carotene, and (C2d) at least one class of compounds selected from reducing compounds and hydrotalcite-like compounds, wherein the reducing compound is dibutyltin dilaurate, and the hydrotalcite-like compound is magnesium aluminometasilicate Al 2 O 3 ·MgO·1.7SiO 2 · n H 2 O. and wherein the stabilizer is at least one selected from: (C2a) a compound represented by formula R A -CO-R D -CO-CHR B R C, wherein R A is a hydrocarbon group, R B and R C are each independently a hydrogen atom or a hydrocarbon group, and R D is a direct bond, a methylene group or a 1,2-ethylene group, (C2b) an ascorbic acid, calciferol, α-tocopherol or quercetin, (C2c) a carotene, and (C2d) at least one class of compounds selected from reducing compounds and hydrotalcite-like compounds, (C2a) a compound represented by formula R A -CO-R D -CO-CHR B R C, wherein R A is a hydrocarbon group, R B and R C are each independently a hydrogen atom or a hydrocarbon group, and R D is a direct bond, a methylene group or a 1,2-ethylene group, (C2b) an ascorbic acid, calciferol, α-tocopherol or quercetin, (C2c) a carotene, and (C2d) at least one class of compounds selected from reducing compounds and hydrotalcite-like compounds, wherein the reducing compound is dibutyltin dilaurate, and the hydrotalcite-like compound is magnesium aluminometasilicate Al 2 O 3 ·MgO·1.7SiO 2 · n H 2 O.