thumb|500px|Districts of the House of Representatives
, the House of Representatives of Japan is elected from a combination of multi-member districts and single-member districts, a method called parallel voting. Currently, 176 members are elected from 11 multi-member districts (called proportional representation blocks or PR blocks) by a party-list system of proportional representation (PR), and 289 members are elected from single-member districts, for a total of 465. 233 seats are therefore required for a majority. Each PR block consists of one or more prefectures, and each prefecture is divided into one or more single-member districts. In general, the block districts correspond loosely to the major regions of Japan, with some of the larger regions (such as Kantō) subdivided.
History
Until the 1993 general election, all members of the House of Representatives were elected in multi-member constituencies by single non-transferable vote. In 1994, Parliament passed an electoral reform bill that introduced the current system of parallel voting in single-member constituencies and proportional voting blocks. The original draft bill in 1993 by the anti-LDP coalition of Prime Minister Morihiro Hosokawa included proportional party list voting on a national scale, an equal number of proportional and district seats (250 each) and the possibility of split voting. However, the bill stalled in the House of Councillors. After the Liberal Democratic Party (LDP) had returned to power later that year, it was changed to include proportional voting in regional blocks only, the number of proportional seats was reduced, but the possibility to cast two separate votes was kept in the bill. The electoral reform law was finally passed in 1994. It was first applied in the 1996 general election.
Redistricting and reapportionment
Amendments to the electoral law in 2002 and 2013 changed the boundaries of single-member districts and reapportioned seats between prefectures (+5/-5 in 2002; +0/-5 in 2013, resulting in a net change of -5 in district seats in the House of Representatives to 295 and overall seats to 475). The borders of the regional proportional blocks have never changed, but the apportionment of seats to the regional proportional blocks changed in 2000 after the number of proportional seats had been reduced from 200 to 180 (reducing the total number of seats in the lower house from 500 to 480), and in the 2002 reapportionment.
Another reapportionment was passed by the National Diet in June 2017. In the majoritarian segment, it will change 97 districts in 19 prefectures, six are eliminated without replacement (one each in Aomori, Iwate, Mie, Nara, Kumamoto and Kagoshima). In the proportional segment, four "blocks" lose a seat each (Tōhoku, N. Kantō, Kinki, Kyūshū). Thus, the number of majoritarian seats is reduced to 289, the number of proportional seats to 176, the House of Representatives overall shrinks to 465. The reform took effect one month after promulgation, on July 16, 2017.
Based on a legal amendment in 2016, the number of electoral districts in each prefecture is currently apportioned according to the Adams method in proportion to the number of voters in the prefecture in the large-scale census conducted every 10 years. Based on the first large-scale census conducted in 2020 after the legal amendment, the single-seat constituency boundaries were revised in the 2022 Election Law amendment. Ten prefectures (Miyagi, Fukushima, Niigata, Shiga, Wakayama, Okayama, Hiroshima, Yamaguchi, Ehime, and Nagasaki) lost one constituency each, while Saitama, Chiba, and Aichi each gained one, Kanagawa gained two, and Tokyo gained five.
Hokkaidō (8 block seats)
The block constituency for Hokkaidō (比例北海道ブロック) elects 8 members proportionally. It contains only Hokkaidō Prefecture, which is divided into 12 single-member districts.
Hokkaidō Prefecture (12 districts)
{| class="wikitable"
|+
!District
!Areas included
!Number of constituents
!Current representative
!Party represented
!Map
|-
|District 1
|Sapporo, wards of Chūō-ku and Minami-ku, parts Nishi-ku and Kita-ku wards
|455,279
|Takahiro Katō
|LDP
|rowspan=6|220px
|-
|District 2
|Sapporo, ward of Higashi-ku and part of Kita-ku ward
|459,952
|Yusuke Takahashi
|Sapporo, wards of Toyohira-ku, Kiyota-ku and part of Shiroishi-ku ward
|462,546
|Hirohisa Takagi
|LDP
|-
|District 4
|LDP
|-
|District 5
|LDP
|-
|District 6
|Cities of Asahikawa, Furano, Nayoro and Shibetsu
Kamikawa Subprefecture
|395,302
|Kuniyoshi Azuma
|LDP
|-
|District 7
|LDP
|rowspan=6|220px
|-
|District 8
|Cities of Hakodate and Hokuto
Hiyama Subprefecture and Oshima Subprefecture
|339,230
|Jun Mukōyama
|LDP
|-
|District 9
|Cities of Date, Muroran, Noboribetsu and Tomakomai
Hidaka Subprefecture and Iburi Subprefecture
|361,963
|Hideki Matsushita
|LDP
|-
|District 10
|LDP
|-
|3rd district
|Cities of Daisen, Nikaho, Semboku, Yokote, Yurihonjō and Yuzawa
Districts of Ogachi and Senboku
|299,529
|Toshihide Muraoka
|LDP
|rowspan=3|286x286px|frameless
|-
|District 2
|Cities of Hachinohe, Misawa and Towada
Part of district of Shimokita
|371,661
|Junichi Kanda
|LDP
|-
|District 3
|Cities of Hirakawa, Hirosaki, Goshogawara, Kuroishi and Tsugaru
Districts of Kitatsugaru, Minamitsugaru, Nakatsugaru and Nishitsugaru
|327,919
|Jiro Kimura
|Cities of Hachimantai, Kamaishi, Kuji, Miyako, Ninohe, Ōfunato, Rikuzentakata, Takizawa, and Tōno<br>Districts of Iwate, Kamihei, Kesen, Kunohe, Ninohe, and Shimohei
|342,912
|Shun'ichi Suzuki
|LDP
| rowspan="5" |350px
|-
|2nd district
|Sendai, wards of Izumi-ku, Miyagino-ku and Wakabayashi-ku
|453,667
|Katsuyuki Watanabe
|LDP
|-
|4th district
|LDP
|-
|3rd district
|Saitama, ward of Iwatsuki-ku
Cities of Kasukabe and Yoshikawa
District of Kitakatsushika (Town of Matsubushi)
|372,652
|Shinako Tsuchiya
|LDP
|}
Tochigi Prefecture (5 districts)
{| class="wikitable"
|+
!District
!Areas included
!Number of constituents
|LDP
|-
|5th district
|Cities of Iida, Ina and Komagane
Districts of Kamiina and Shimoina
|270,927
|Ichiro Miyashita
|LDP
|-
|3rd district
|Cities of Himi, Imizu, Nanto, Oyabe, Takaoka, and Tonami
|349,960
|Keiichiro Tachibana
|Ishin
|-
|18th district
|Cities of Izumi, Izumiōtsu, Kishiwada, and Takaishi
District of Senboku
|426,329
|Takashi Endo