 This study consisted of two parts. In Treatment Period I, FK949E or placebo was administered orally in a blind manner to bipolar disorder patients with major depressive episodes, with the aim of evaluating the superiority of FK949 over placebo and the dose response of two doses of FK949E based on changes in Montgomery-Asberg Depression Rating Scale MADRS total score. In Treatment Period II, the long-term safety, efficacy and pharmacokinetics of FK949E was evaluated in patients completed the Treatment Period I. Results are reported for Treatment Period I. 