Provided is a separating agent comprising a carrier and a ligand fixed on a surface of a carrier by chemical bonding, in which the carrier is a core-shell particle formed of a non-porous core and a porous shell, the shell having a pore diameter of 9 nm or more and formed of a hydrolysate of polyalkoxysiloxane, and the ligand is an optically active polymer, optically inactive polyester, protein, nucleic acid, or optically active organic compound with a molecular weight of 50 to 1000.