This study consists of a single-dose period (Cycle 0 lasting 3 days) and a multiple-dose period (from Cycle 1 onwards, each cycle lasting 21 days). To compare the PK between ASP8273 Capsules and ASP8273 Capsules A, enrolled subjects will receive a single oral dose of ASP8273 Capsules A on Day 1 of Cycle 0 in the single-dose period and will then be observed for 3 days (including the day of dosing). In the multiple-dose period, subjects will receive multiple oral doses of ASP8273 Capsules during each cycle lasting 21 days. From the viewpoint of PK comparison (bioavailability [BA] evaluation) between ASP8273 Capsules and ASP8273 Capsules A, data from approximately 15 subjects are sufficient for the evaluation. Therefore, if PK data of approximately 15 subjects included in BA evaluation are obtained and the sponsor judges that further acquisition of PK data is not necessary, the single-dose period will not be conducted in subjects who are enrolled thereafter (subjects not included in BA evaluation). Subjects will continue to receive treatment with ASP8273 until they meet the discontinuation criteria.