To provide a copolymer useful as a pigment dispersant, etc., which can form a pigment dispersion useful for an inkjet ink, coloring agent for color filter, or the like.

The copolymer (D) comprises a methacrylic polymer unit (A) having at least one group represented by general formula (1) (wherein R is a hydrogen atom or an ester residue with a valence of n, n is a number of 1-4, Y is a methacrylic polymer) at the terminal, and an aromatic vinyl monomer unit (B), wherein the mass ratio of the unit (A) and the unit (B) is A:B=5-95:95-5.