Study to Find Maintenance Dose for Periodic Administration of ASP3550

Inclusion Criteria: * Histologically proven prostate cancer (adenocarcinoma) of all stages * A patient in whom endocrine treatment is indicated. Patients with rising serum PSA after having prostatectomy or radiotherapy performed with curative intention * Serum testosterone level above 2.2 ng/mL * An ECOG (Eastern Co-operative Oncology Group) P.S. (Performance Status) score of 0 to 2 * Serum PSA level above 2 ng/mL Exclusion Criteria: * Previous or present endocrine treatment for prostate cancer. However, patients who have undergone neoadjuvant/adjuvant endocrine therapy for a maximal duration of 6 months and in whom prostatectomy or radiotherapy was terminated at least 6 months * Treated with a 5α-reductase inhibitor * A candidate for curative therapy, i.e., radical prostatectomy or radiotherapy within 12 months * Concurrent or a history of severe liver disease * Abnormal ECG such as long QTc * A patient receiving ASP3550 in past times * Administered drug in another clinical study or a post-market clinical study in the 28 days prior to the study