Prime Minister Yukio Hatoyama told reporters Wednesday he started thinking about stepping down up to 10 days ago.

In footage aired in the evening by NHK, ex-Prime Minister Junichiro Koizumi meanwhile said, "(The next) prime minister will be the 16th since (1989)."

Koizumi, who served for five years from April 2001, said, "You may say 'change, change,' but this is too many."

Hatoyama said the same night: "I made the decision believing my resignation would be in the national interest. I started thinking about it over seven days ago."

Hatoyama said he first expressed his intention to resign during Monday's meeting with Democratic Party of Japan Secretary General Ichiro Ozawa and Upper House heavyweight Azuma Koshiishi.

Hatoyama is the fourth prime minister to step down in four years. Shinzo Abe served from September 2006 to September 2007, then Yasuo Fukuda served till September 2008, followed by Taro Aso, who exited last September.