Chief cabinet secretary Yosihide Suga, 71, had formally submitted his candidacy for the Liberal Democratic Party leadership last week.
The chief government spokesman faces two younger contenders, former defence minister Shigeru Ishiba and former foreign minister Fumio Kishida, both 63.
The winner of the in-party vote on September 14 will eventually become Japan’s next prime minister because of the ruling bloc’s majority in the parliament.
Mr Abe is stepping down for health reasons.
Mr Suga is a latecomer favoured among party heavyweights as the best candidate to continue Mr Abe’s policies and have reportedly lined up to support him in hopes of getting favourable party and cabinet posts in his government.
Newspaper opinion surveys have also shown Mr Suga surpassing the former favourite Mr Ishiba among the public.
Mr Suga pledged to carry out the challenges left behind by Mr Abe, including measures on the coronavirus, the economic fallout and pursuing the Japan-US security alliance.
Mr Ishiba, who has long been seen as Mr Abe’s rival, is vying for the party leadership for the fourth time, calling for a change to the “Abenomics” economic measures to focus more support for small businesses and low-income earners as well as rural areas.
Mr Kishida, who is currently serving the party policy chief, says he seeks to be a leader who listens to the people’s voices more carefully than Mr Abe and prioritise economic policies to address disparities.
