The present invention relates to a novel polypeptide having affinity for proteins partially including a CH1-CL domain forming a non-native three-dimensional structure and capable of being suitably used for detecting, immobilizing, or removing these proteins and relates to use of the polypeptide. Specifically, disclosed are a polypeptide consisting of an amino acid sequence represented by any one of the following formulas 1 to 3: (1) P-Q-x-I-x-L-x-[IL]-[NT]-[YW] (SEQ ID NO: 1), (2) Y-D-P-E-T-G-T-W-P-Q-x-I-x-L-x-[IL]-[NT]-[YW] (SEQ ID NO: 4), and (3) P—N-S-G-G-G-G-S-Y-D-P-E-T-G-T-W-P-Q-x-I-x-L-x-[IL]-[NT]-[YW] (SEQ ID NO: 7) (wherein x represents an amino acid residue; and brackets represent any one of the amino acid residues within the brackets), and a method of using the polypeptide to detect, purify, or remove a protein partially including a CH1-CL domain forming a non-native three-dimensional structure.