This is an open label, non-randomized, phase II study of eltrombopag in combination with rabbit ATG/CsA in subjects with moderate or more severe AA who have not received prior ATG/ALG-based immunosuppressive therapy. The objective is to assess additive effects of eltorombopag on overall response rate (ORR) at 6 months (Week 26) of treatment with ATG/CsA. Subjects will be assessed at least weekly for safety during the period from the start of ATG/CsA to 4 weeks after the start of administration of eltrombopag. After that, subjects will visit every 2 weeks until Week 26. Subjects in whom the treatment is assessed as effective at Week 26 may continue treatment with eltrombopag after 6 months when clinically indicated at the discretion of the investigator. There are five follow-up visits: at discontinuation of the treatment of eltrombopag, and Weeks 1, 2, 3, 4 and 26 after treatment discontinuation. As this study is the first Japanese phase II study in which this product is administered in combination with ATG/CsA to subjects with naive moderate or more severe AA, the subject number of this study is determined to be 10 based on the feasibility survey.