A polymer crosslinking agent which comprises a (meth)acrylic-based graft silicone which has a main chain having (meth)acrylic-based repeating units represented by the following formulae, and, and a side chain having an unsaturated bond(s) and an organopolysiloxane structure: wherein, R 1 s each independently represent a hydrogen atom or a methyl group, A represents an alkoxy group having 1 to 22 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms which may contain one or more kinds selected from -O-, -S- and -NR-, where R represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms, provided that the oxygen atom, the sulfur atom and the nitrogen atom are not adjacent to each other, an amino group, a dialkylsiloxy group, a halogen atom or a hydroxyl group; B is a 2-allyloxyethoxy group; C represents any of a group having a linear organopolysiloxane structure represented by the following formula, or a group having a dendritic organopolysiloxane structure represented by the following formula or: in the formula, Z 1 represents a divalent organic group, R 3 s each independently represents a saturated hydrocarbon group having 1 to 10 carbon atoms or a phenyl group, R 4 represents a saturated hydrocarbon group having 1 to 10 carbon atoms, and "m" is an integer of 0 to 100; in the formulae and, Z 2 represents a divalent organic group, "a" is a number of 0 to 3, Q represents a group represented by the following formula, D represents an organopolysiloxanyl group having a dendritic structure with a hierarchical number of "c" and a valence of 3 c + 1, that is, "3 to the c th power" + 1, "c" is an integer of 1 to 8, R 5 represents a saturated hydrocarbon group having 1 to 10 carbon atoms or a phenyl group; R 6 represents a saturated hydrocarbon group having 1 to 8 carbon atoms or a phenyl group; R 7 represents a hydrogen atom, a saturated hydrocarbon group having 1 to 10 carbon atoms or a phenyl group, a 2 is a real number of 0 to 2, and "n" is an integer of 2 to 12; an order of bonding of the repeating units represented by the formulae, and is not limited, "p", "q" and "r" are integers, "q" and "r" are not 0, and are numbers in which a number average molecular weight measured by gel permeation chromatography using polystyrene as a standard substance of the polymer crosslinking agent becomes 1,000 to 1,000,000 g/mol. wherein, R 1 s each independently represent a hydrogen atom or a methyl group, A represents an alkoxy group having 1 to 22 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms which may contain one or more kinds selected from -O-, -S- and -NR-, where R represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms, provided that the oxygen atom, the sulfur atom and the nitrogen atom are not adjacent to each other, an amino group, a dialkylsiloxy group, a halogen atom or a hydroxyl group; B is a 2-allyloxyethoxy group; C represents any of a group having a linear organopolysiloxane structure represented by the following formula, or a group having a dendritic organopolysiloxane structure represented by the following formula or: an amino group, a dialkylsiloxy group, a halogen atom or a hydroxyl group; B is a 2-allyloxyethoxy group; C represents any of a group having a linear organopolysiloxane structure represented by the following formula, or a group having a dendritic organopolysiloxane structure represented by the following formula or: in the formula, Z 1 represents a divalent organic group, R 3 s each independently represents a saturated hydrocarbon group having 1 to 10 carbon atoms or a phenyl group, R 4 represents a saturated hydrocarbon group having 1 to 10 carbon atoms, and "m" is an integer of 0 to 100; in the formulae and, Z 2 represents a divalent organic group, "a" is a number of 0 to 3, Q represents a group represented by the following formula, D represents an organopolysiloxanyl group having a dendritic structure with a hierarchical number of "c" and a valence of 3 c + 1, that is, "3 to the c th power" + 1, "c" is an integer of 1 to 8, R 5 represents a saturated hydrocarbon group having 1 to 10 carbon atoms or a phenyl group; R 6 represents a saturated hydrocarbon group having 1 to 8 carbon atoms or a phenyl group; R 7 represents a hydrogen atom, a saturated hydrocarbon group having 1 to 10 carbon atoms or a phenyl group, a 2 is a real number of 0 to 2, and "n" is an integer of 2 to 12;