The objective of this study is to confirm the safety of ATGAM in patients with moderate to severe aplastic anemia under the actual use in Japan. The registration criteria is patients with moderate to severe aplastic anemia who receive ATGAM. The observation period is 24 weeks (6 months) from the start of administration (Day 1). However, in cases where treatment has been completed or discontinued less than 24 weeks after the start of administration, observation is continued until completion (discontinuation) of treatment.