Abstract: In Japanese academia, the relationship between pre-World War II Japanese political parties and bureaucrats has traditionally been seen as one of opposition. However, during the late Meiji era to the early Taisho era, a distinct political system known as the “Kei-En System” emerged. This system saw Katsura Taro, representing the domain-based bureaucrats, and Saionji Kinmochi, the president of the Rikken Seiyūkai (Association of Friends of Constitutional Government), taking turns in power for 12 years. The “Kei-En System” reflected a nuanced political structure that went beyond mere confrontation, incorporating elements of coordinated cooperation between political parties and bureaucrats. This paper delves into the insights provided by the Hara Takashi Diary to analyze the concepts behind the reforms of official appointment system and their implementation by Hara Takashi, who was also the president of the Rikken Seiyūkai. It demonstrates how Hara successfully brought numerous experienced bureaucrats into the folds of the Rikken Seiyūkai and implemented reform measures, including broadening the scope for making appointments to highgrade senior officials. These measures not only expanded the Rikken Seiyūkai‘s influence to encompass antiparty domain-based bureaucrats,but also hastened the trend of bureaucrats joining political parties and running for elected positions-an occurrence referred to as the “bureaucratic partyization”.At the same time, by continuing the strategy of “bureaucratic partyization” that had been in place since the Kei-En era, Hara absorbed a large number of senior officials with administrative experience into the Rikken Seiyūkai (Association of Friends of Constitutional Government), thus reserving administrative talents for the transition to party politics.

Key words: Hara Cabinet, reforms of official appointment system, parliamentary under secretary, bureaucratic partyization, the Privy Council