Early exit polls are projecting a win for Prime Minister Shinzo Abe's ruling bloc in the upper house of parliament. The victory would give Japan its first long-term premier since 2006.
Poll booths closed at 8 p.m. local time (1100 GMT), with 242 seats in the upper chamber of parliament up for grabs.
Based on exit polls, Japanese broadcaster NHK predicted that Abe's Liberal Democratic Party (LDP) and its junior coalition partner New Komeito would win a majority of seats.
With approval ratings of more than 60 percent since winning elections in December, Abe is expected to see a confident victory for the LDP. The conservative prime minister appealed to voters ahead of the vote, vowing to implement an economic policy that will lift Japan out of its 15 years of deflation.
His supporters say controlling both of the country's chambers will remove political obstacles to his agenda and give him free rein to begin less popular reforms. Those reforms, the third part of an economic policy dubbed "Abenomics," will target the labor market to make the hiring and firing of employees easier, and include participation in a large free trade pact and a consumption tax increase.
Abe's economic policy has pushed down the value of the yen and triggered a rise in the stock market. However, his opponents say that the popular "Abenomics" plan is simply a way for the prime minister to gain support and win both houses of parliament, allowing him to implement his conservative social agenda.
There are also concerns Abe could shift the country away from its pacifist constitution and boost its military, a move likely to test already anxious relationships with China and South Korea – two nations currently locked in a territorial dispute with Japan.
Should the LDP and its junior coalition partner win a strong majority in Sunday's vote, it would give the country its first long-term prime minister since Junichiro Koizumi left office in 2006.
The following year the Abe-led LDP suffered a heavy defeat, losing control of the upper house for the first time in the party's history. The loss allowed the opposition to block policy and Abe stepped down two months later citing ill health.
dr,rc/jm (AFP, dpa, Reuters)