In March 1951, Iwatani was selected by the Japan national team for its first game after World War II, the 1951 Asian Games. He debuted at this competition on March 7 against Iran. On March 9, he scored two goals against Afghanistan during the match for third place and Japan won 2-0. He also played in the 1954 Asian Games. He played as captain in June 1956 at the 1956 Summer Olympics qualification against South Korea. Japan finished with one win and one defeat. After the qualifiers, the team drew lots for captain, and he was selected. The team won the qualification for the 1956 Summer Olympics. However, in November, he was not selected by the Japan team for the Olympics. He played eight games and scored four goals for Japan until 1956.