The purpose of the invention is to provide an antibody which recognizes OPN N-half but does not recognize the full-length OPN, and its use. A monoclonal antibody which is characterized in that it recognizes a protein or polypeptide in which the C-terminal amino acid sequence is YGLR (SEQ ID NO: 1) and it substantially does not recognize a protein or polypeptide which has an amino acid sequence of YGLR outside of the C-terminal, as well as a method for measuring OPN N-half utilizing the said antibody, a method for diagnosing diseases relating to OPN N-half, a method for judging the severity of said disease, and a method for treating said diseases, are provided.
