A carrier which may have excellent pressure resistance, and even when a protein ligand is not immobilized thereon, a high dynamic binding capacity to a target substance, and a high performance of separating a target substance from a biological sample. Such a carrier may include a polymer having a crosslinked structure containing a divalent group of formula (1): wherein R1 to R4 are independently a single bond or divalent hydrocarbon group, R5 and R6 are independently H or a hydrocarbon group, X is a thio group, sulfinyl group, sulfonyl group, oxy group, >N(—R31), >Si(—R32)2, >P(—R33), >P(═O)(—R34), >B(—R35), or >C(—R36)2 (R31 to R36 independently being H or hydrocarbon group), and * is a bond, provided that when both R1 and R3 or both R2 and R4 are a divalent hydrocarbon group, respectively, R1 and R3 or R2 and R4 may form a ring together with an adjacent carbon atom.