[Problem] Provided is an anti-human Igβ antibody which crosslinks BCR and FcγRIIb and has an immunosuppressive function more enhanced than that of an antibody in the prior art. [Means for Solution] An anti-human Igβ antibody comprising a heavy chain variable region comprising CDR1 consisting of the amino acid sequence of amino acid numbers 31 to 35 of SEQ ID NO: 2, CDR2 consisting of the amino acid sequence of amino acid numbers 50 to 65 of SEQ ID NO: 2, and CDR3 consisting of the amino acid sequence of amino acid numbers 98 to 108 of SEQ ID NO: 2, a light chain variable region comprising CDR1 consisting of the amino acid sequence of amino acid numbers 24 to 38 of SEQ ID NO: 4, CDR2 consisting of the amino acid sequence of amino acid numbers 54 to 60 of SEQ ID NO: 4, and CDR3 consisting of the amino acid sequence of amino acid numbers 93 to 101 of SEQ ID NO: 4, and a heavy chain constant region which is a human Igγ1 constant region having amino acid mutations of S239D, H268D, and L328W.
