Disclosed are: a peptide capable of binding to an immunoglobulin; a fusion protein of the peptide; nucleic acids encoding the peptide and the fusion protein, respectively; production methods for the peptide and the fusion protein, respectively; a composition and a means for binding an immunoglobulin; a pharmaceutical composition for the treatment or prevention of a disease induced by the binding between C1q and an immunoglobulin, which comprises a peptide capable of binding to the immunoglobulin or a fusion protein of the peptide; and others.