The present invention relates to: a polypeptide that includes an antigen-binding domain and a carrying section having an inhibitory domain for inhibiting the antigen-binding activity of the antigen-binding domain, said polypeptide having a half-life longer than that of the antigen-binding domain when existing alone； a production method and a screening method for said polypeptide； a pharmaceutical composition containing said polypeptide； a production method and a screening method for a single-domain antibody, the antigen-binding activity of which is inhibited by being associated with a specific VL/VH/VHH； and a library of fused polypeptides including a single-domain antibody, the antigen-binding activity of which is inhibited by being associated with a specific VL/VH/VHH.
