Prime Minister Sanae Takaichi said the 15-member expert group will examine emergency scenarios, defence budgets and funding as tensions rise with China, North Korea and Russia.
The review supports Takaichi's push to speed Japan's military buildup, after her cabinet last week removed restrictions on lethal weapons exports despite domestic and Chinese criticism.
Japan's 2022 strategy targeted defence spending of 2% of GDP, or 43 trillion yen by 2027, but the government says it has already reached that level and may consider further increases.
Will Japan's new defense strategy and closer U.S. ties transform its pacifist identity, or provoke fresh challenges at home and abroad?
Could Japan's rapid military buildup and push to revise Article 9 trigger a new arms race in East Asia, or strengthen regional stability?