2023 Ōita at-large district by-election was held on 23 April 2023 because Kiyoshi Adachi resigned as a member of the House of Councillors.

In 2019 election, Kiyoshi Adachi, an independent recommended by four opposition parties, including the Former CDP, defeated Yōsuke Isozaki, a current member of the House of Councillors belonging to the Liberal Democratic Party, and was elected for the first time in Ōita at-large district.

[2] Adachi announced his candidacy for Ōita Prefecture gubernatorial election and resigned as a member of the House of Councillors on March 10, 2023.

The LDP has nominated Aki Shirasaka, the owner of Inaba, a club in Ginza, as its candidate.

[5] After the assassination of Shuzo Abe, the LDP's collusion with the Unification Church was discovered, and the match drew national attention as it was a one-on-one battle between the ruling and opposition parties amid falling approval ratings of the Kishida administration.