The present invention provides an epitope recognized by an antibody (hereinafter, also referred to as an anti-ADAMTS-13 antibody) against a cleaving protease (hereinafter, also referred to as ADAMTS-13) specific to von Willebrand factor (hereinafter, also referred to as vWF), and a polypeptide comprising the epitope region. The present invention also provides a polypeptide located in a region from position 449 to position 687 in an amino acid sequence composing the ADAMTS-13, which is recognized by the anti-ADAMTS-13 antibody, or a peptide fragment derived from the polypeptide.