Kei-En era (or Kei-On era) was the 8-year period from 1905 to 1912 during which Taro KATSURA, who belonged to the faction led by Aritomo YAMAGATA of the Imperial Japanese Army, and Kinmochi SAIONJI, who assumed the position of president of Rikken seiyukai (a political party) as a successor of Hirobumi ITO, gained power alternately.
桂園時代（けいえんじだい/けいおんじだい）とは、大日本帝国陸軍・山縣有朋閥に属する桂太郎と、伊藤博文の後継者として立憲政友会総裁に就いた西園寺公望が、政権を交互に担当した1905年から1912年の8年間をいう。