Taro Aso has emerged as the early front-runner to replace Japanese Prime Minister Yasuo Fukuda, following his shock resignation on Monday.
Mr Aso, who is secretary general of the ruling Liberal Democratic Party (LDP), said he was "qualified to take over Mr Fukuda's agenda".
The PM is stepping down after only a year in office, amid plunging support.
The LDP will hold a vote on 22 September for a new president, who would then become the prime minister.
The opposition says parliament should be dissolved and a snap election called.
Mr Aso, 67, became secretary general of the LDP only last month.
This would be his fourth attempt to secure the party's top job.
An outspoken conservative, Mr Aso has called for Japan to play a more prominent role on the world stage.
He is a charismatic figure known for his love of manga comics, but he is also prone to gaffes and has had to apologise in the past for a number of controversial statements.
Mr Aso is the only lawmaker to have openly expressed his intention to run in the leadership contest so far.
Other potential contenders could include Yuriko Koike, a former defence minister, Seiko Noda, the consumer affairs minister and Kaoru Yosano, the economics minister.
Campaigning for the leadership election is set to begin on 10 September.
Yasuo Fukuda made his announcement late on Monday night.
He is the second prime minister in a row to step down after less than 12 months in office, and Japanese media denounced his unexpected resignation.
It was "unmistakably cowardly", the Asahi Shimbun said in an editorial. "This only goes to show that Fukuda himself and the LDP do not possess the fundamental strength to effect a breakthrough in the difficult political situation."
Mr Fukuda's administration has been chronically unpopular. Lost pension records, a controversial health insurance scheme and a sliding economy have all contributed to his woes.
But the main problem has been the battle with the upper house. The opposition controls the chamber, which means it is in a position to block legislation.
Last month Mr Fukuda reshuffled his cabinet in an attempt to boost his flagging popularity. He has also recently announced a 11.7-trillion-yen ($107bn) economic stimulus package.
But these measures failed to boost cabinet approval ratings, which had been below 30% for several months.
Japan's next general election must be held no later than September 2009.
But, correspondents say, whoever takes over will face pressure to call an immediate general election.
Yukio Hatoyama, of the opposition Democratic Party of Japan, said polls were the only answer.
"We should immediately dissolve the parliament and put our trust in the people," he said.