日本民主黨於2009 年的眾議院選舉中擊敗執政的自由民主黨，黨魁鳩 山由紀夫於9 月16 日成為日本首相。由於民主黨在參議院未過半，為了維 持國會穩定運作，鳩山首相選擇與社會民主黨、國民新黨組成聯合內閣。 不過鳩山政權內部不斷出現閣員之間的對立，而鳩山首相始終無法處理 這些政府決策過程之中所發生的混亂，學者與主要媒體多認為，發生混亂的 原因是在於鳩山本人的領導能力不足。不過本論文認為，導致鳩山政權內部 的混亂主因是民主黨建構的決策運作模式本身存在的缺陷。本論文透過分析 日本首相的領導能力，並以郵政改革法案與普天間基地移設問題進行案例研 究證明了這個假設。

Yukio Hatoyama, the chairman of the Democratic Party of Japan （DPJ）, succeeded to the Prime Minister of Japan on 16 September 2009 after DPJ won the 2009 Japanese general election. In the election, DPJ acquired 308 out of a total of 480 seats in the House of Representatives of Japan, while the Liberal Democratic Party（LDP）, the former ruling party only acquired 119 seats. However, Hatoyama was thus forced to form a coalition government with the Social Democratic Party and the People’s New Party in response to a situation where DPJ does not have a majority in the House of Councilors. Hatoyama seemed to be unable to effectively manage the discrepancies and integrate different opinions in his government. It is suggested by many researchers and mass media that Hatoyama does not possess strong leadership, which may lead to the political chaos in his team. This research therefore employs the cases of the the Reexamining Postal Privatisation Bills and the Futenma deal to investigate the leadership and the decision-making mechanisms in Hatoyama’s government. It is found that the inefficiency of the ‘politician-led government’ decision-making model developed by DPJ might be the main reason of the political chaos.