Mr. Ishiba was elected as leader of the LDP party on September 27, replacing Prime Minister Fumio Kishida, who resigned on the morning of October 1.
New Prime Minister Ishiba will announce a new cabinet later on October 1 and plans to call a parliamentary election on October 27.
"I believe it is important to let the new administration receive public evaluation as soon as possible," AP quoted Mr. Ishiba as announcing plans to call a snap election after he was formally elected prime minister. He is expected to dissolve parliament on October 9 ahead of the election campaign.
In August, then-Prime Minister Fumio Kishida said he would step down at the end of his three-year term to pave the way for a new leader before the next national election, as corruption scandals dogged his party and government.
Mr. Kishida and his ministers resigned at a cabinet meeting on the morning of October 1. Mr. Kishida left office after a brief farewell ceremony, in which he was presented with a bouquet of red roses and applauded by staff and former Cabinet members.
“As we face a critical moment at home and abroad, I earnestly hope that important policies that pioneer Japan's future will be vigorously pursued by the new Cabinet,” Kishida said in a statement.
Meanwhile, on September 30, Mr. Ishiba announced the LDP leaders before announcing the Cabinet. Former Environment Minister Shinjiro Koizumi, who came third in the race for the party leadership, will head the party's election task force.
The new prime minister is expected to have two former defense ministers in his cabinet: Takeshi Iwaya as foreign minister and Gen Nakatani as defense minister.
Most of the new cabinet members, including Prime Minister Ishiba, are not expected to be affiliated with factions led and controlled by influential party figures.
The liberal Asahi newspaper said Mr Ishiba's lack of a stable power base could also make his government fragile, although the new prime minister hopes to build party unity as he prepares for the upcoming election.
Mr. Ishiba has proposed an Asian version of the NATO military alliance and more discussions among regional partners on the use of U.S. nuclear deterrents.
He also proposed a more equal Japan-US security alliance, including joint management of US bases in Japan and having Japanese Self-Defense Forces bases in the US.
Prime Minister Ishiba proposed combining existing security and diplomatic groupings, such as the Quad and other bilateral and multilateral frameworks involving the United States, Australia, New Zealand, South Korea and the Philippines.
He pledged to continue former Prime Minister Kishida's economic policies to lift Japan out of deflation and achieve real wage growth, while addressing challenges such as Japan's falling birthrate and population and its resilience to natural disasters.
Mr. Ishiba, first elected to parliament in 1986, has served as defense minister, agriculture minister and other key Cabinet posts, and was LDP secretary-general under Mr. Shinzo Abe.
