Liberal Democratic Party Secretary General Taro Aso has a support rate of 50.7 percent in the LDP's presidential election, while former Defense Minister Yuriko Koike, 56, is a distant second with 8.1 percent.
The poll was conducted Saturday and Sunday by telephone on LDP members eligible to vote in the election. The survey results are based on 1,445 valid responses.
Aso and Koike are followed by former LDP policy chief Nobuteru Ishihara, 51, at 7.5 percent, economic and fiscal policy minister Kaoru Yosano, 70, at 5.1 percent, and former Defense Minister Shigeru Ishiba, 51, at 3.5 percent.
Aso is the leading choice in 45 of the 47 prefectures, while Koike is ahead in her home district of Tokyo and Ishiba in his Tottori district.
If these numbers hold up, Aso would win the election in just one round of voting.
In another estimate last week, he was expected to secure more than 200 votes among the LDP's 387 Diet members. Yosano was second with about 50 votes.