當一個國家的政治體制越民主時，其地方分權亦會越徹底，則聯邦制的傾向就越明顯。日本近年來致力於推動地方分權改革，同樣出現是否全面性地將國家體制由單一國轉型為聯邦國的議題。本研究以新制度主義為研究途徑，探討日本推動廣域自治體合併的思絡、方法、及諸問題。

The more democratic a country becomes, the more decentralization develops, and the more obvious tendency of federal state. Similarly, as a unitary state, Japan that promotes the decentralization reforms faces with this problem. Therefore, this paper is a case study on the schemes and methods of the merger of prefectures in Japan's decentralization reforms.