Sources close to the Japanese Prime Minister say he plans to step down to deal with a health problem.
Abe Shinzo is scheduled to hold a news conference later in the day to explain his decision.
Abe has visited a hospital twice over the past two weeks, fuelling speculation that his health has deteriorated.
This is the second time that Abe is to leave the post over a medical issue -- stepping down in 2007, because of his inflammatory bowel disease, after only serving a year in office.
He returned to the top job in 2012 after a landslide election win in the Lower House.
This seven-year tenure makes him Japan's longest-serving leader ever.
Abe could have served one more year in office. His term as president of the main ruling Liberal Democratic Party would have run out in September next year. (NHK)