Backgrounder: Japan's House of Representatives electoral system

Voting on Japan's House of Representatives, or the lower house of parliament, is held on Sunday. The following are some facts about Japan's lower house electoral system:

-- The House of Representatives has a total of 480 seats, comprising 300 in single-seat districts and 180 under the proportional-representation system in 11 regional blocks.

-- Citizens aged 20 or older are eligible to vote in the lower house election, while those aged 25 or older are eligible to run for election to the house with four-year term.

-- Each voter casts two ballots -- one to choose a candidate in a single-seat constituency and the other to choose a political party or group for proportional representation.

-- Political groups and parties submit lists of their candidates for the proportional representation voting system beforehand, and will be given seats in accordance with their share of block votes. They will then grant the block seats to candidates in the order of the lists.

-- Under the current system, a candidate who runs in a single-seat district can also appear in the proportional representation voting list. But to do so, the candidate must belong to a political party which has five or more Diet members or which gained 2 percent or more of the total valid votes in the previous general election.