Itagaki entered the Imperial Japanese Army Academy, where he befriended numerous notable Japanese military figures including Yasuji Okamura, Kenji Doihara, and Tetsuzan Nagata. Itagaki graduated from the Army Academy in 1904 and fought in the Russo–Japanese War. Itagaki married Kikuko Ogoshi, the daughter of his former mentor Kenkichi Ogoshi who died in the Battle of Mukden.