A compound represented by the general formula below, in which the core (X) below and the terminal group (Y1) below are bonded to each other: [Chem. 1] X (Y1) n 1 wherein in the general formula , n 1 represents the number of terminal groups (Y1) bonded to the core (X), and n 1 is equal to the valence of the core (X); and the terminal group (Y1) is a phosphorus-containing group represented by the general formula below, a phosphorus-containing group represented by the general formula below, a (meth)acryloyl group-containing group (Y2) represented by the general formula below, a (meth) acryloyl group, a C 1-20 hydrocarbon group or a hydrogen atom, and a plurality of terminal groups (Y1) may be the same as or different from each other, with the proviso that among all the terminal groups (Y1) in the compound represented by the general formula , one or more terminal groups are phosphorus-containing groups represented by the general formula below or phosphorus-containing groups represented by the general formula below, and one or more terminal groups are (meth)acryloyl group-containing groups (Y2); wherein in the general formula , one end of the group is bonded to the core (X), and the other end of the group is bonded to the core (X) present in another compound represented by the general formula ; and wherein in the general formula , R 4a represents a hydrogen atom or a methyl group, R 4b represents a C 2-6 linear alkylene group, or a C 2-6 linear oxyalkylene group, and the linear alkylene group or the linear oxyalkylene group is optionally substituted with a C 1-6 alkyl group or a (meth)acryloyloxymethylene group in place of a hydrogen atom; and wherein the core (X) is at least one selected from the group consisting of groups represented by the general formulas to below: wherein in the general formula , n 5g is an integer of 1 to 40. wherein in the general formula , n 1 represents the number of terminal groups (Y1) bonded to the core (X), and n 1 is equal to the valence of the core (X); and the terminal group (Y1) is a phosphorus-containing group represented by the general formula below, a phosphorus-containing group represented by the general formula below, a (meth)acryloyl group-containing group (Y2) represented by the general formula below, a (meth) acryloyl group, a C 1-20 hydrocarbon group or a hydrogen atom, and a plurality of terminal groups (Y1) may be the same as or different from each other, with the proviso that among all the terminal groups (Y1) in the compound represented by the general formula , one or more terminal groups are phosphorus-containing groups represented by the general formula below or phosphorus-containing groups represented by the general formula below, and one or more terminal groups are (meth)acryloyl group-containing groups (Y2); wherein in the general formula , one end of the group is bonded to the core (X), and the other end of the group is bonded to the core (X) present in another compound represented by the general formula ; and wherein in the general formula , R 4a represents a hydrogen atom or a methyl group, R 4b represents a C 2-6 linear alkylene group, or a C 2-6 linear oxyalkylene group, and the linear alkylene group or the linear oxyalkylene group is optionally substituted with a C 1-6 alkyl group or a (meth)acryloyloxymethylene group in place of a hydrogen atom; and wherein the core (X) is at least one selected from the group consisting of groups represented by the general formulas to below: wherein in the general formula , n 5g is an integer of 1 to 40. <EOS>