Abstract: In Japan, administrative reforms and changes of the ruling system of the Liberal Democratic Party are closely related. Within the LDP where the process of administrative reforms are intertwined with changes of its power structure, different personal performances of politicians usually lead to changes of their status and power, and in the early years of the 21st century the postal privatization reform has resulted in the rise and fall of each factional force. From the perspective of the process of decisionmaking, administrative reforms have continuously advanced the institutionalization of the mode of decision making characterized by the domination of prime minister, but their effectiveness has been affected by various factors. The impact of administrative reforms on the social support base of the Liberal Democratic Party is complex. In the face of an increasingly diversified civil society, it is difficult for the LDP regime to solidify its social support base through administrative reforms.

Key words: administrative reforms, the Liberal Democratic Party regime, domination of prime minister, Japans party system