Provided are: a conjugated block copolymer capable of increasing the amount of optical absorption by a photoelectric conversion active layer and controlling the morphology thereof and capable of achieving excellent photoelectric conversion efficiency; and a photoelectric conversion element comprising a composition including an electron accepting material using this kind of conjugated block polymer.A π-electron conjugated block copolymer comprises: a polymer block (A) and a polymer block (B), each of which involves a monomer unit having at least one fused π-conjugated skeleton including at least one thiophene ring in one part of the chemical structure thereof, the polymer block (A) and the polymer block (B) have different monomer units from each other.