A novel copolymer having excellent pigment dispersion performance, and more particularly, a novel copolymer usable as a pigment dispersing agent that can attain high luminance and high contrast of a green picture element in a color filter. The novel copolymer contains: a block chain (A) including a repeating unit having a tertiary amino group; and a block chain (B) including a repeating unit represented by the following formula (I) (wherein R1 represents a hydrogen atom or a C1-C3 alkyl group, R2 and R3 each independently represent a hydrogen atom or a C1-C6 alkyl group, Q represents an oxygen-containing saturated hetero ring group optionally having an alkyl group as a substituent or a C2-C20 alkenyl group, and n represents an integer of 0 to 6), and has an amine value of 80 mgKOH/g or more and 250 mgKOH/g or less.