From December 2001 to September 2005, Takasu served as Ambassador Extraordinary and Plenipotentiary at the Permanent Mission of Japan to International Organizations in Vienna.
(including the International Atomic Energy Agency (IAEA), the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty (CTBTO) and the United Nations Industrial Development Organization (UNIDO)).
During this period, he held the position of President of the IAEA General Conference and he chaired the Preparatory Commission for the CTBTO.
During the Gulf crisis, Takasu was in charge of formulating Japan’s contribution to the international efforts, including drafting UN Peacekeeping Cooperation Law.
He joined Japan’s diplomatic service in 1969, subsequently serving in various overseas posts (London, Kuala Lumpur, New York, Jakarta, Vienna, and Washington, DC).