The Socialist Democratic Federation (社会民主連合, Shakai-minshu-rengō) (SDF), also referred to in Japanese by the shortened Shaminren (社民連), was a Japanese political party that existed from 1978 to 1994. It was formed from the merger of the Socialist Citizen's Federation (社会市民連合, Shakai-shimin-rengō) and the Shakai Club (社会クラブ, Shakai-kurabu).

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The Socialist Democratic Federation was a splinter party of the Japan Socialist Party (JSP). Its emergence followed a series of upheavals involving this left-wing, opposition political party, which began with the establishment of the Democratic Socialist Party in January 1960 and the later reemergence of the Japan Communist Party (JCP). The exodus of its membership is partly attributed to the perceived pro-Communist tendencies on the part of the JSP leadership during the political crisis involving the revision of Japan's Mutual Security Treaty with the United States.^[4] Experts also blame a diminished public support for the socialist party, particularly in big cities.^[4] The process continued until the next decade when the Shaminren finally split off from JSP. By this time, JSP was already in severe disarray it was ridiculed as Ni-hon (two-volumed) Shokaito (socialist party).^[5]

The Socialist Democratic Federation became part of the non-liberal coalition that elected Morihiro Hosokawa as Japan's Prime Minister in 1993.^[6] During this election, the Shaminren obtained 0.7 percent share of the vote, securing four seats in the Japanese House of Representatives.^[7]

• Hideo Den (March 1978 – February 1985)
• Satsuki Eda (February 1985 – May 1994)

• Democratic Party of Japan
• Japan New Party
• Naoto Kan
• New Party Sakigake
• New Frontier Party