An object of the present invention is to provide a novel copolymer useful as a dispersing agent for a pigment or the like. The novel copolymer contains: a block chain (A) comprising at least one repeating unit selected from the group consisting of a repeating unit having a tertiary amino group and a repeating unit having a quaternary ammonium salt group; and a block chain (B) comprising a repeating unit having an acidic group and a repeating unit represented by the following formula (I) (wherein R 1 represents a hydrogen atom or a C1-C3 alkyl group; and R 2 represents an aliphatic hydrocarbon group or an alicyclic hydrocarbon group), wherein the repeating unit represented by formula (I) has a copolymerization ratio of 90 mass% or more in the block chain (B).
