Provided is a cyclic peptide that is represented by formula (I) or formula (I'), has excellent antibody-binding characteristics, and also has improved drug stability. Also provided are an affinity chromatography support, a labeled antibody, an antibody-drug conjugate, and a pharmaceutical preparation. RN-Xg-[Xi-Xa-Xm-X1-X2-X3-Xn-Xb-Xj]k-Xh-RC...(I) In formula (I): Xa and Xb each independently represents an amino acid residue derived from an amino acid that has a thiol group in a side chain thereof other than L-cysteine and D-cysteine, Xa and Xb each being bonded via a disulfide bond； or one of Xa and Xb represents an amino acid residue derived from an amino acid that has a thiol group in a side chain thereof other than L-cysteine and D-cysteine and the other represents an amino acid residue derived from an amino acid that has a haloacetyl group in a side chain thereof, Xa and Xb each being bonded via a thioether bond. RN-Xg-[Xi-Xa-Xm-X1-X2-X3-Xn-Xb-Xj]k-Xh-RC...(I') In formula (I'): one of Xa and Xb represents an amino acid residue derived from L-cysteine or D-cysteine and the other represents an amino acid residue derived from an amino acid that has a haloacetyl group in a side chain thereof, Xa and Xb each being bonded via a thioether bond； or one of Xa and Xb represents an amino acid residue derived from L-penicillamine or D-penicillamine and the other represents an amino acid residue derived from an amino acid that has a haloacetyl group in a side chain thereof, Xa and Xb each being bonded via a thioether bond.
