A coating agent comprising a compound represented by formula: wherein A represents wherein R 1 represents an electron-donating group, a represents an integer of 0 to 5, and a' represents an integer of 0 to 7, Z represents a carbon atom or a silicon atom, R 2 represents a hydrogen atom, a hydroxyl group, a linear or branched C1 to C6 alkyl group, a linear or branched C1 to C6 alkoxy group, a C3 to C6 cyclic alkyl group, or a C3 to C6 cyclic alkoxy group, X represents, when Z is a carbon atom: • a C1 to C20 alkylene group optionally comprising an oxygen atom, a sulfur atom, a selenium atom, -NR- with R representing a hydrogen atom or a C1 to C6 alkyl group, a C3 to C6 divalent aliphatic ring group, a C6 to C10 arylene group, an amide structure or a urethane structure; • a C3 to C10 divalent aliphatic ring group; • or a C6 to C10 arylene group; X represents, when Z is a silicon atom: • a C1 to C20 alkylene group optionally comprising an oxygen atom, a sulfur atom, a selenium atom, -NR- with R representing a hydrogen atom or a C1 to C6 alkyl group, an amide structure or a urethane structure, Y represents -O-CO- m2 -CR=CH2 with m2 representing 0 or 1 and R representing a hydrogen atom or a methyl group; -CH=CH2; an allyloxy group; an allyloxycarbonyloxy group; an epoxy group; n represents an integer of 2 or 3, m represents an integer of 1 or 2, 1 represents an integer of 0 or 1, and n + m + 1 = 4; and when n represents an integer of 2 or 3, A is the same or different. A represents wherein R 1 represents an electron-donating group, a represents an integer of 0 to 5, and a' represents an integer of 0 to 7, Z represents a carbon atom or a silicon atom, R 2 represents a hydrogen atom, a hydroxyl group, a linear or branched C1 to C6 alkyl group, a linear or branched C1 to C6 alkoxy group, a C3 to C6 cyclic alkyl group, or a C3 to C6 cyclic alkoxy group, X represents, when Z is a carbon atom: • a C1 to C20 alkylene group optionally comprising an oxygen atom, a sulfur atom, a selenium atom, -NR- with R representing a hydrogen atom or a C1 to C6 alkyl group, a C3 to C6 divalent aliphatic ring group, a C6 to C10 arylene group, an amide structure or a urethane structure; • a C3 to C10 divalent aliphatic ring group; • or a C6 to C10 arylene group; • a C1 to C20 alkylene group optionally comprising an oxygen atom, a sulfur atom, a selenium atom, -NR- with R representing a hydrogen atom or a C1 to C6 alkyl group, a C3 to C6 divalent aliphatic ring group, a C6 to C10 arylene group, an amide structure or a urethane structure; • a C3 to C10 divalent aliphatic ring group; • or a C6 to C10 arylene group; X represents, when Z is a silicon atom: • a C1 to C20 alkylene group optionally comprising an oxygen atom, a sulfur atom, a selenium atom, -NR- with R representing a hydrogen atom or a C1 to C6 alkyl group, an amide structure or a urethane structure, • a C1 to C20 alkylene group optionally comprising an oxygen atom, a sulfur atom, a selenium atom, -NR- with R representing a hydrogen atom or a C1 to C6 alkyl group, an amide structure or a urethane structure, Y represents -O-CO- m2 -CR=CH2 with m2 representing 0 or 1 and R representing a hydrogen atom or a methyl group; -CH=CH2; an allyloxy group; an allyloxycarbonyloxy group; an epoxy group; n represents an integer of 2 or 3, m represents an integer of 1 or 2, 1 represents an integer of 0 or 1, and n + m + 1 = 4; and when n represents an integer of 2 or 3, A is the same or different.