自第二次世界大戰結束後，日本眾議院選舉制度從1947年以來採用中選舉區制度，直到1993年眾議院大選後，除了日本共產黨以外的7個在野政黨一同組成聯合政府，結束了自由民主黨自1955年以來的長期執政，情況開始所轉變。日本新黨黨魁細川護熙就任日本首相後，為了兌現選舉承諾，而在任內推動了選舉制度改革，將選制改為小選舉區比例代表並立制，期望能以此改善國內政治獻金醜聞頻傳的金權政治弊端。而實施新選舉制度後所帶來的諸如小選舉區制有利於大型政黨但一黨難以過半、小黨在國會生存難度增加卻也有比例代表區維持其存在等效應，導致聯合政府從1990年代開始不再只是為了達成某種政治目標而形成的少數特例。自此以後，日本政黨結盟組成聯合政府便形成一種常態。因此本研究認為，1990年代選舉制度改革與聯合政府的形成，兩者可說是相輔相成。 為了進一步分析選舉制度改革對1990年代的日本聯合政府、乃至於日本政壇造成何種影響，本研究將以1996年小選舉區比例代表並立制首度實踐於眾議院選舉作為分水嶺，將1996年以前成立的細川、村山聯合政府定義為「選舉制度改革前的聯合政府」，1996年到2000年成立的橋本、小淵與森聯合政府定義為「選舉制度改革後的聯合政府」，並從政黨規模、意識形態、政黨穩定狀況與政治資金規正法修正案的實施等角度進行觀察與比較。本研究發現，選舉制度改革後的聯合政府在政黨規模上已形成一個大型政黨加上兩個小黨的合作模式，意識形態也趨向右派主導而多元。就政黨穩定狀況而言，經過選舉制度改革所帶來的政黨重組，使日本政黨正走向稍無定型的一強，或是二強n弱體制。而在政治資金規正法修正案與選舉制度改革雙管齊下實施後，日本選舉也已由過去的派閥主導，開始向政黨主導模式邁出了第一步。 / After the end of World War II, SNTV-MMD system (single non-transferable vote with multi-member district system) was adopted by the Lower House in Japan since 1947. However, the electoral system of Lower House has been adapted after the Japanese general election in 1993. The Liberal Democratic Party, generally abbreviated to “LDP,” has been the ruling party of Japan since it was founded in 1955, but the LDP lost its overall majority after the Japanese general election in1993. A coalition government was created by seven opposition political parties, and Morihiro Hosokawa, the leader of Japan New Party, was elected prime minister. Hosokawa promoted electoral reform, he adapted the electoral system of Lower House for single member district with proportional representation system, because he promised to eradicate the plutocracy in Japan. The new electoral system causes several conditions, including the major parties are superiors in election, but it’s difficult for them to win the majority seats in Lower House. Besides, it’s difficult for the minor parties to win the seats in single member district, but there is an opportunity for them to win seats in proportional representation. Those conditions cause that Japanese political parties form coalition government become normality. Therefore, the electoral reform and the forming of coalition government are complementarity in the 1990s. In this research, the coalition governments in the 1990s are divided into two groups by the executing of single member district with proportional representation system in Japanese general election of 1996. The Hosokawa government and the Murayama government are defined as “the coalition governments before the executing of new electoral system.” The Hashimoto government, the Obuchi government and the Mori government are defined as “the coalition governments after the executing of new electoral system.” Those two group are contrasted with each other from the scale of political parties, the ideology, the stability of political parties, and executing of the Political Funds Control Law. There four major findings in this research. The first one is the coalition governments after the executing of new electoral system are formed by one major party and two minor parties. The second one is even the coalition governments after the executing of new electoral system are leading by the right-wing parties, the ideology of them is multivariate. The third one is electoral reform causes the party realignment and the Japanese political party system become one unstable major party or two major parties with several minor parties. The last one is the leader of Japanese election is turning to the parties from factions, because the new electoral system and the Aamendment to the Political Funds Control Law are executed.