A curable composition comprising: at least one polyfunctional (meth)acrylamide compound selected from the group consisting of a compound represented by General Formula and a compound represented by General Formula; and at least one betaine monomer selected from the group consisting of compounds represented by General Formula to, in General Formula, R's each independently represent a hydrogen atom or a methyl group, and L's each independently represent -O-, an alkylene group having 2 to 4 carbon atoms, or a divalent linking group formed by combining these. in General Formula, R 1 's each independently represent a hydrogen atom or a methyl group, R 2 and R 4 each independently represent -O-, an alkylene group having 1 to 4 carbon atoms, a divalent linking group formed by combining these, R 3 represents -O-, an alkylene group having 1 to 4 carbon atoms, a group represented by General Formula, or a divalent linking group formed by combining these, and L 1 and L 2 each independently represent a single bond or a group represented by General Formula, in General Formula, R 31 represents a hydrogen atom or a methyl group, and the symbol "*" represents a bonding site, in General Formula, R 41 represents a methyl group, an ethyl group, an n-propyl group, or an i-propyl group, and a plurality of R 41 's may be the same as or different from each other, R 42 represents a hydrogen atom or a methyl group, R 43 represents -NH- or -O-, n4 represents an integer of 1 to 4, 14 represents an integer of 1 to 4, and M 4 represents SO 3- or COO -, in General Formula, R 51 represents a methyl group, an ethyl group, an n-propyl group, or an i-propyl group, and a plurality of R 51 's may be the same as or different from each other, R 52 represents a hydrogen atom or a methyl group, n5 represents an integer of 1 to 4 and two n5's may be the same as or different from each other, L 51 represents a linear or branched alkylene group having 3 or 4 carbon atoms and two L 51 's may be the same as or different from each other, and M 5 represents SO 3- or COO -, and two M 5 's may be the same as or different from each other, and in General Formula, R 62 represents a hydrogen atom or a methyl group, R 63 represents -NH- or -O-, and n6 represents an integer of 1 to 4. at least one polyfunctional (meth)acrylamide compound selected from the group consisting of a compound represented by General Formula and a compound represented by General Formula; and at least one betaine monomer selected from the group consisting of compounds represented by General Formula to, in General Formula, R's each independently represent a hydrogen atom or a methyl group, and L's each independently represent -O-, an alkylene group having 2 to 4 carbon atoms, or a divalent linking group formed by combining these. in General Formula, R 1 's each independently represent a hydrogen atom or a methyl group, R 2 and R 4 each independently represent -O-, an alkylene group having 1 to 4 carbon atoms, a divalent linking group formed by combining these, R 3 represents -O-, an alkylene group having 1 to 4 carbon atoms, a group represented by General Formula, or a divalent linking group formed by combining these, and L 1 and L 2 each independently represent a single bond or a group represented by General Formula, in General Formula, R 31 represents a hydrogen atom or a methyl group, and the symbol "*" represents a bonding site, in General Formula, R 41 represents a methyl group, an ethyl group, an n-propyl group, or an i-propyl group, and a plurality of R 41 's may be the same as or different from each other, R 42 represents a hydrogen atom or a methyl group, R 43 represents -NH- or -O-, n4 represents an integer of 1 to 4, 14 represents an integer of 1 to 4, and M 4 represents SO 3- or COO -, in General Formula, R 51 represents a methyl group, an ethyl group, an n-propyl group, or an i-propyl group, and a plurality of R 51 's may be the same as or different from each other, R 52 represents a hydrogen atom or a methyl group, n5 represents an integer of 1 to 4 and two n5's may be the same as or different from each other, L 51 represents a linear or branched alkylene group having 3 or 4 carbon atoms and two L 51 's may be the same as or different from each other, and M 5 represents SO 3- or COO -, and two M 5 's may be the same as or different from each other, and in General Formula, R 62 represents a hydrogen atom or a methyl group, R 63 represents -NH- or -O-, and n6 represents an integer of 1 to 4.