PROBLEM TO BE SOLVED: To provide a multi-specific antigen-binding molecule having alternative function to F.VIII which is a cofactor enhancing an enzymatic reaction.SOLUTION: There are provided various types of bi-specific antibodies, each of which can bind to both blood coagulation factor IX/activated blood coagulation factor IX and blood coagulation factor X specifically and has an alternative function to a blood coagulation factor VIII cofactor function, i.e., a function of enhancing the activation of blood coagulation factor X by an activated blood coagulation factor IX. From among the antibodies, a multi-specific antigen-binding molecule having high activity and having an alternative function to the function of blood coagulation factor VIII is successfully found.【課題】酵素反応を増強する補因子であるF.VIIIの機能を代替する機能を有する多重特異性抗原結合分子の提供。【解決手段】血液凝固第IX因子/活性化血液凝固第IX因子及び血液凝固第X因子の双方に特異的に結合し、血液凝固第VIII因子の補因子機能、すなわち活性化血液凝固第IX因子による血液凝固第X因子活性化を促進する機能を代替する機能を有する種々の二重特異性抗体を作製した。これらの抗体の中から、血液凝固第VIII因子の機能を代替する活性の高い多重特異性抗原結合分子を見出すことに成功した。【選択図】なし