It reacts with human immunoglobulin M uniquely, it designates that immunology measuring method which uses the anti- human immunoglobulin M monoclonal antibody and the particular monoclonal antibody which can form the immunity cohesion body which in solution state is based on the antigen antibody reaction with human immunoglobulin M is offered as topic. In addition, offer of immunology measuring method where the non unique reaction which originates in the inhibiter and the human immunoglobulin M which control the non unique reaction which originates in the human immunoglobulin M which cannot obstruct with law until recently is controlled is designated as topic. The new monoclonal antibody where it designates the reactivity in solution state as evaluation figure at the time of sorting the monoclonal antibody which reacts to human immunoglobulin M, human immunoglobulin M it is possible in 1 types, can achieve practical immunity cohesion measurement to cohere, profit and the aforementioned topic were solved.ヒト免疫グロブリンMと特異的に反応し、溶液状態でヒト免疫グロブリンMとの間で抗原抗体反応に基づく免疫凝集体を形成できる抗ヒト免疫グロブリンMモノクローナル抗体及び当該モノクローナル抗体を使用する免疫学的測定方法を提供することを課題とする。また、従来法では阻止できないヒト免疫グロブリンMに起因する非特異反応を抑制する抑制剤及びヒト免疫グロブリンMに起因する非特異反応が抑制された免疫学的測定方法の提供を課題とする。ヒト免疫グロブリンMに反応するモノクローナル抗体の選別において、溶液状態での反応性を評価指標とし、1種類でヒト免疫グロブリンMを凝集することができ、実用的な免疫凝集測定を達成できる新規のモノクローナル抗体を得、前記課題を解決した。