Prime Minister Shinzo Abe is to meet with former Osaka Mayor Toru Hashimoto on Saturday night at a Tokyo hotel, a political source said, only a day after the populist mayor left office declaring he is retiring from politics.

Also set to attend the meeting are Chief Cabinet Secretary Yoshihide Suga and Osaka Gov. Ichiro Matsui, who heads the political party "Initiatives from Osaka" that he formed in October with Hashimoto after both left Ishin no To (Japan Innovation Party), the source said.

Hashimoto, a lawyer who is expected to serve as a legal adviser to the new party he headed until Dec. 12, shares the same views as Abe on seeking to revise the Constitution. They last met in June.

Ahead of the House of Councilors' election set for next summer, the meeting is giving rise to speculation that Hashimoto will play a role in pushing for constitutional reform since Matsui has said his party aims to be part of the two-thirds or more of all lawmakers of each house whose concurring votes are required to initiate amendments to the supreme law.