The Japanese Society on Thrombosis and Hemostasis published the guidelines for the treatment of acquired hemophilia A in November 2011 to promote its early diagnosis and appropriate therapy. Successively, the disease was more readily recognized, and a revised version of the guidelines was published in December 2017. Bleeding in patients with acquired hemophilia A is typically more severe than that in patients with congenital hemophilia A. An analysis using the global coagulation assay revealed that the hemostatic function of the plasma of patient with acquired hemophilia A is extremely low, even if factor VIII activities are retained; we present the presumed mechanism for the same. Regarding immunosuppressive therapy to eliminate inhibitors, a large-scale data analysis of patients enrolled in Europe reported that prednisolone (PSL) monotherapy or combination therapy with PSL and cyclophosphamide is the first-line therapy for this disorder, supporting the recommended therapy mentioned in Japan's guidelines. This study aims to highlight the revised guidelines and the latest findings on pathophysiology, diagnosis, and therapy of acquired hemophilia A.