Media surveys suggest the Democratic Party of Japan (DPJ) could win by a landslide over the Liberal Democratic Party (LDP) that has ruled for most of the past 50 years, although some analysts say those predictions may be excessive.
A DPJ victory in the lower house election would break a deadlock in parliament, where the opposition and its allies won control of the less powerful upper chamber in 2007. Financial markets would generally welcome an end to the political stalemate.
"I don't like what's going on now in this country. Things have to change," said Kazuya Tsuda, a 78-year-old retired doctor in Tokyo who voted for the Democratic Party.
Japanese media will announce the results of exit polls after voting ends at 8 pm (1100 GMT). Later in the evening they will issue further projections based on partial vote counts.
Reuters