The Prime Minister of Japan, Junichiro Koizumi, will be challenged by one of his fiercest critics in the race later this month for the leadership of the ruling Liberal Democratic Party.
Shizuka Kamei, a senior party figure, is the first parliamentarian to challenge the Prime Minister for the leadership.
The election is crucial because whoever wins the presidency is almost certain to become premier of Japan, as this post is chosen by lawmakers in a parliament dominated by the ruling party.
On Tuesday, a former transport minister, Takao Fujii, also announced he was entering the race.
Mr Kamei has been a sharp critic of government financial policy, and announced his candidacy pledging to undo all of the Prime Ministers work to limit public investment in the economy.
From the newsroom of the BBC World Service