Provided is an antibody that has a high binding activity to membrane-bound IgM on the surface of B cells even in the presence of secretory IgM in blood and exerts a growth inhibitory effect on B cells. Bispecific antibodies that bind to IgM and B cell surface antigens.血中の分泌型IgM存在下であっても、B細胞表面の膜結合型IgMとの結合活性が高く、B細胞に対し増殖阻害効果を発揮する抗体の提供。 IgM及びB細胞表面抗原に結合する二重特異性抗体。