The present invention pertains to: a polypeptide that includes an antigen-binding domain and a conveying section having an inhibitory domain for inhibiting the antigen-binding activity of the antigen-binding domain, and that has a half-life longer than that of the antigen-binding domain when existing alone； a production method and screening method for the polypeptide； a pharmaceutical composition containing the polypeptide； a production method and 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.
