Ozawa's Democrats have been looking increasingly likely to win an election that must be held by October, ending more than 50 years of nearly unbroken rule by Prime Minister Taro Aso's Liberal Democratic Party.
"I myself have done nothing of which to be ashamed and the actions of my secretary were carried out properly in accordance with the political funding law and properly dealt with," Ozawa told a news conference.
"Therefore, it is not a matter of me doing this or that," he said, when asked whether he would step down.
The Democrats have been ahead in opinion polls.
Aso, whose popular support has dropped below 10 percent in one poll and is not much higher in others, is struggling to keep his own job and has faced calls from within his party to step down before the election.
Speculation about Aso's future grew when the finance minister quit last month, after being forced to deny he was drunk at a G7 news conference in Rome.
Güncelleme Tarihi: 04 Mart 2009, 11:54