Bajrang, who came into the Asian Games as favourite to win the gold in this category, beat his Japanese opponent 11-8 in the final bout.
The 24-year-old Indian had won three consecutive gold medals -- CWG (Gold Coast), Tbilisi Grand Prix (Georgia) and Yasar Dogu International (Istanbul) -- ahead of the Asian Games.
En route to his gold medal bout, Bajrang defeated Khasanov Sirojiddin (Uzbekistan), Fayziev Abdulqosim (Tajikistan) and Batchuluun Batmagnai (Mongolia).