As a result of producing ACE910 mutants in which various sites of the constant region were modified, a bispecific antibody having higher FVIII-like activity than ACE910 was found. In addition, the present inventors have identified a mutation site that enhances FVIII-like activity and a method for enhancing FVIII-like activity using the mutation.定常領域の様々な部位を改変したACE910変異体を作製した結果、ACE910よりも高いFVIII様活性を有する二重特異性抗体を見出した。また、FVIII様活性を高める変異位置の同定、その変異を用いたFVIII様活性を高める方法を見出した。