The Social Democratic Party of Japan (シャクヮイ ミンシュトウ; 社會民主黨 Shakwai Minshuto) is a Japanese political party founded in 1920 and being the part of the National Front with the Nationalist Party of Japan since its foundation.
The Social Democratic Party was originally formed as the Reorganized Social Democratic Party (サイ ヘンセイ ミョウミ シャクヮイ ミンシュトウ; 再編成社會民主黨 Sai Hensei Shakwai Minshuto), an attempt to unify all left-minded political parties in Japan into one "big tent party" and to revive the original Social Democratic Party that established in 1901. The Reorganized SDP was formed through the merger of the right wing of the Japanese Socialist Party, the Japanese Agrarian Party, the Society for Enlightenment, and the Fabian Society in Japan.
In 1921, during the time of "First Political Consolidation" (1920-1925), the SDP dropped its "Reorganized" word from its official name and renamed itself as the Social Democratic Party of Japan. Within the Front, the Social Democrats is the only party that represents the left-wing elements among other Front parties. During the "Second Political Consolidation" (1945-1950), many members of the Social Democrats joined the reorganized Nationalist Party of Japan under General Katobushi Toshio. There were many attempts since 1947 to merge the Social Democrats with the Nationalists to establish a new political balance, however its were never came to fruition.