Japanese Prime Minister Shinzo Abe has won a majority in the upper house, exit polls suggest.
His Liberal Democratic Party and its junior partner New Komeito were set to get at least 71 of the 121 seats being contested, broadcaster NHK projected.
This would give him control of both houses of parliament for the first time in six years.
Mr Abe said the expected result was an endorsement of his economic reforms, as he seeks to end long-term stagnation.
The deadlock in parliament has been seen as a key factor in Japan's recent "revolving door" of prime ministers.
Official results are not expected until Monday.
But the exit poll suggested Mr Abe's coalition would control 130 seats in the 242-seat upper house. Half the seats were being contested in Sunday's election.
The result is being seen as a vote of confidence in Mr Abe, says the BBC's Rupert Wingfield-Hayes in Tokyo.
He has the power - the question is whether he has the will, too, says our correspondent.
Media reports said voter turnout was lower than in the last upper house election, in 2010.Search for stability
Mr Abe said his party's economic policies were having a positive impact.
The result may have been expected, but this is still a big and significant victory for Japan's ruling party and Prime Minster Shinzo Abe.
Mr Abe came to power last December vowing to drag Japan out of 20 years of stagnation. He launched a risky and aggressive stimulus plan designed to push down the value of the Japanese Yen, and boost exports.
It appears to be working. But now comes the hard part. To keep Japan growing Mr Abe must implement painful and unpopular structural reforms, raise taxes and open Japan's economy to more competition.
Today's election victory will give him the power to do so. The question is whether he has the will.
"Our economic policy is right. This is what I have said and I expect the support of our people," he said.
"These policies are contributing to the economy already and further improvement is needed, including wage increases, more consumption, more investments."
Japan's upper chamber, while not as powerful as the lower house, is able to block legislation introduced by the government.
Opposition parties have had enough combined seats to control the upper chamber in recent years, leading to what has become known as a "twisted parliament".
This has resulted in factionalism and multiple changes of prime minister.
"We need political stability to carry out policies," Mr Abe said ahead of the vote.
Mr Abe, 58, has relatively strong public support for his proposals for economic reform, which seek to revive the economy, stagnant for two decades.
Since his coalition government came to power, the economy has grown by 4% and the stock market by more than 40%.
His first two measures involved a big injection of cash by the Bank of Japan and a major boost in government spending.
But he now faces the task of driving through difficult structural changes to the economy.
Trade barriers need to come down, taxes will need to rise and large parts of the economy will have to be deregulated.
One of the decisions he will have to make later this year is whether to raise sales tax next April from 5% to 8% to help reduce Japan's national debt.
Mr Abe is also considering whether to cut Japan's 36% corporate tax to spur growth and open up the power industry, currently controlled by regional monopolies.
And his government is keen to join a free trade agreement known as the Trans-Pacific Partnership (TPP), being negotiated by 11 countries.
Mr Abe is also thought likely to endorse several controversial policies beyond the economy.
These include restarting Japan's nuclear reactors - something many in Japan are opposed to.
A possible revision of Japan's pacifist constitution, especially a section which prohibits the use of force in international disputes except for self-defence, may also be a priority. But correspondents say pursuing nationalistic policies may cause tension with neighbouring countries.