General elections were held in Japan on November 9, 2003. Incumbent Prime Minister Junichiro Koizumi and the Liberal Democratic Party won the most seats in the House of Representatives but failed to secure a majority. The main opposition Democratic Party made considerable gains, winning 177 of the 480 seats in the House of Representatives, its largest share ever. Other traditional parties like the Communist Party and the Social Democratic Party lost substantial numbers of seats, marking the start of a newly consolidated two-party system in Japanese politics, which would end in 2012 with the emergence of Japan Restoration Party.
On October 11, 2003, following his re-election as leader of the Liberal Democratic Party on September 20, Prime Minister Junichiro Koizumi dissolved the House of Representatives of Japan's Diet. This action was in accordance with Article 7 of the Constitution of Japan, which grants the Prime Minister the authority to dissolve the lower house after consulting the Emperor.
This election marked the first since Koizumi assumed the role of Prime Minister in April 2001. The primary contenders were the Liberal Democratic Party (LDP) and the Democratic Party (DPJ). The LDP continued to enjoy robust support in rural regions and among the elderly, largely due to substantial agricultural subsidies, while the DPJ was more popular with younger voters and in urban centers. Nonetheless, the LDP was favored due to the disproportionate influence of less populated rural districts within Japan's electoral framework.
Key issues addressed by the candidates included the persistent economic recession, known as the Lost Decades; reforms to the public pension system; the level of Japan's involvement in Iraq in support of the U.S.; relations with North Korea; and the privatization of Japan Post Holdings and highways in the Tokyo area.
The preceding general election for the Lower House occurred in June 2000 under the leadership of Prime Minister Yoshiro Mori.
National newspapers have reported that the recent election was more favorable to the Democratic Party (DPJ) than to the Liberal Democratic Party (LDP). The DPJ secured a plurality of votes and added 40 seats, becoming the largest opposition party with 177 seats in the lower house. Within the ruling coalition, only New Kōmeitō saw an increase, raising its membership from 31 to 34. Despite Prime Minister Koizumi's high approval ratings, the LDP did not gain additional seats, leading some analysts to view Koizumi as a weakened Prime Minister. However, others note that several non-partisan members were actually aligned with the LDP, including Kato Koichi, suggesting the LDP effectively maintained its seat count.
The LDP was successful in rural regions, whereas the DPJ excelled in urban centers. Voter turnout was 59.86%, marking it the second-lowest since 1945. The new house members had an average age of 51.03 years, which is 3.2 years younger than the previous election's average. A majority of the new members, 302, were born post-1945. Post-election, the number of women in the lower house fell to 34 from the previous 35.
Early poll data and exit polls underscored the impact of swing voters, who comprised 18% of the electorate. The Asahi Shimbun reported that over half of these voters chose the DPJ. Exit polls initially produced varied forecasts, with one predicting the DPJ would secure as many as 230 seats, over 50 more than the actual outcome.
The Liberal Democratic Party did not secure a majority on its own, necessitating the continuation of its coalition with New Kōmeitō and the New Conservative Party.