It is intended to provide an antibody specific to HbA1c, antibody-producing cells capable of supplying the antibody in a stable state in the future, and a method of constructing the antibody-producing cells without any probability factors, and a method which comprises fusing mouse spleen cells, which have been sensitized with an immunogen composed of a compound containing the following structural formula (I) and a binding protein, with a myeloma-origin cell line, obtaining monoclonal antibody-producing cells by cloning, and then purifying and acquiring the monoclonal antibody produced by these cells into the culture supernatant ##STR00001##