Ohkoshi served in Tokyo Metropolitan Police Department for 20 years, including a three-year assignment to the Consulate General of Japan in New York as a consul. There he had opportunities to work with law enforcement experts from the Federal Bureau of Investigation and the New York Police Department, acquiring experience of the world's highest level of security management. In 1987, he joined Exxon Mobil to establish its security function. Then he moved on to JP Morgan and to AIG (American International Group) as regional security manager of Japan and Korea. He is a steering committee member of the US State Department's OSAC（Overseas Security Advisory Council）Japan Branch, and a director of the Japan Society of Security Management. He is a leading figure in Japan in security and crisis management.