The purpose of this essay is, firstly, to analyze how the Japanese government coped with the international situation before the Fukuda Doctrine was announced and how the government aimed at a continuation of détente and secondly, to evaluate the essence and significance of the doctrine, with a greater focus on Mr. Fukuda's diplomatic idea, namely omnidirectional-peace diplomacy. The doctrine was announced during his visit to Southeast Asia in August 1977. The basic principles are (1) to reject the role of a major military power, (2) to establish reliable relationships with Southeast Asian countries, and (3) to contribute to the building of peace and prosperity throughout Southeast Asia by cooperating with ASEAN and its member countries in their own efforts to strengthen their solidarity and resilience, while aiming at fostering a relationship based on mutual understanding with the nations of Indochina.<br>The essay consists of five sections. In the first section, I review the international circumstances surrounding the Fukuda Doctrine, where so-called “détente” and unstable international relations were mixed. In the second section, I review the omni-directional-peace diplomacy which Mr. Fukuda advocated. Based on the US-Japan relationship, this policy was intended for friendly relationships with all countries, refusing to be a major military power. And this idea was a major influential factor in making the basic nature of the doctrine. Japan's intention to overcome the structure of the cold war was also another influential factor for the doctrine. In the third and fourth sections, I explain concretely how relationships with ASEAN and the countries of Indochina were established before the Fukuda Doctrine was announced. Mr. Fukuda's insight and leadership, together with the accumulation of steady contacts with those countries by officials of the Ministry of Foreign Affairs, enabled the announcement of such diplomatic policies for Southeast Asia. In the fifth section, I review the essence and significance of the Fukuda Doctrine. The doctrine stabilized international relations directly after the Vietnam War. It consolidated the foundation of Japan's diplomacy for Southeast Asia and strengthened the feeling of togetherness among free nations. Though Japan could not prevent the diffusion of Soviet-China enmity to Indochina and the new cold war in 1980s, the doctrine left a legacy for Japan's diplomacy and international society after the cold war