|Japanese name||Shakai Minshu-t?|
|Founded||19 January 1996|
|Headquarters||2-4-3-7F Nagata-cho, Chiyoda-ku, Tokyo 100-0014|
|International affiliation||Socialist International|
|House of Councillors|
|House of Representatives|
|Prefectural assembly members|
|Municipal assembly members|
The Social Democratic Party (, Shakai Minshu-t?, often abbreviated to Shamin-t?) is a political party in Japan that was established in 1996. Since its reformation and name change in 1996, it has advocated pacifism and defined itself as a social-democratic party. It was previously known as the Japan Socialist Party (, Nihon Shakait?, abbreviated to JSP in English).
The party was refounded in January 1996 by the majority of legislators of the former Socialist Party of Japan which was Japan's largest opposition party in the 1955 System. However, most of the legislators joined the Democratic Party of Japan after that. Five leftist legislators who did not join the SDP formed the New Socialist Party which lost all its seats in the following elections. The SDP enjoyed a short period of government participation from 1993 to 1994 as part of the Hosokawa cabinet and later formed a coalition government with the Liberal Democratic Party under 81st Prime Minister Tomiichi Murayama of the JSP from 1994 to January 1996. The SDP was part of ruling coalitions between January and November 1996 (First Hashimoto Cabinet) and from 2009 to 2010 (Hatoyama Cabinet).
In 1995, the former Japan Socialist Party (JSP) was in a deep crisis. Aiming at saving the party, the leadership of JSP decided to dissolve the party and to establish a new social democratic party. In January 1996, such a new party, the Social Democratic Party was established along with the dissolution of JSP. De jure, JSP changed its name to the Social Democratic Party (SDP) as an interim party for forming a new party. However, a movement for transforming the SDP into a new social-democratic and liberal party was unsuccessful. Under Murayama's successor Ry?tar? Hashimoto (LDP), the SDP remained part of the ruling coalition. Long before the disappointing result in the 1996 Japanese general election, the party lost the majority of its members of the House of Representatives, mainly to predecessors of the Democratic Party of Japan (DPJ) that was formed in 1996, but also some to the NFP and other opposition parties. After its electoral defeat in the 1996 general election when it lost another 15 of its remaining 30 seats in the lower house, the SDP left the ruling coalition which it had entered as the second largest force in Japanese politics as a minor party.
The SDP won six seats in the 2003 Japanese general election, compared with 18 seats in the previous 2000 Japanese general election. Its motives against the Self-Defense Forces have reverted into abolishing it in the long term, returning into its opposition against the force it had applied in the 1950s. Doi had been the leader since 1996, but she resigned in 2003, taking responsibility for the election losses. Mizuho Fukushima was elected as the new party leader in November 2003. In the 2004 Japanese House of Councillors election, the SDP won only two seats, having five seats in the House of Councillors and six seats in the House of Representatives. In 2006, the party unexpectedly gained the governorship of the Shiga Prefecture. In the 2009 Japanese general election, the DPJ made large gains and the SDP maintained its base of 7 seats in the, becoming a junior partner in a new government coalition. However, disagreements over the issue of the Futenma base led to the sacking of Fukushima from the cabinet on 28 May and the SDP subsequently voted to leave the ruling coalition.
As of October 2010, the SDP had six members in the House of Representatives and four members in the House of Councillors. Following the 2012 Japanese general election, the party retained only six seats in the whole of the Diet, two in the House of Representatives and four in the House of Councillors. The count lowered to five seats in 2013. In 2013, the party's headquarters in Nagatacho, where the party's predecessor the JSP had moved in 1964, were demolished. The headquarters moved to a smaller office in Nagatacho.
During the nomination period of the 2016 Japanese House of Councillors election, the party signed an agreement with the Democratic, Communist and People's Life parties to field a jointly-endorsed candidate in each of the 32 districts in which only one seat is contested, thereby uniting in an attempt to take control of the House from the LDP/Komeito coalition. The party had two Councillors up for re-election and fielded a total of 11 candidates in the election, 4 in single and multi-member districts and 7 in the 48-seat national proportional representation block.
In the 2017 Japanese general election, the party managed to hold to its two seats it had prior to the election. Tadatomo Yoshida declined to run for re-election when his term expired in January 2018. Seiji Mataichi was elected unopposed in the ensuing leadership election and took office on 25 February 2018.
On 14 November 2020, the party voted to agree to a merger arrangement with the Constitutional Democratic Party (CDP), allowing members to leave the SDP and join the latter party. The majority of the party supported the agreement and thus joined the CDP. However, party leader Fukushima herself was opposed to the merger agreement and thus remains a member of the Social Democratic Party.
||Constituency / title||Term of office||Election results||Photo||(term)|
|Took office||Left office|
|Preceding party: Japan Socialist Party (left-wing)|
|Chair of the Social Democratic Party (1996-present)|
|19 January 1996||28 September 1996||-||Hashimoto |
(coalition, confidence and supply)
|28 September 1996||15 November 2003||-|
|15 November 2003||25 July 2013||-|
|Hatoyama Y. |
30 May 2010)
(until 28 July 2019)
|25 July 2013||14 October 2013||-|
(until 25 July 2016)
(29 July 2019 - present)
|14 October 2013||25 February 2018|
(until 28 July 2019)
|25 February 2018||22 February 2020|
|22 February 2020||present|
PR block votes
PR block votes
|1996||Takako Doi||1,240,649||2.2||3,547,240||6.4||LDP-SDP-NPS coalition (1996-1998)|
|2009||Mizuho Fukushima||1,376,739||2.0||3,006,160||4.3||DPJ-PNP-SDP coalition (2009-2010)|
Up for re-election in 2022