Japan’s nuclear disarmament and non-proliferation policy is largely shaped by responses to the international environment and domestic social and political environment. Contrast between security and anti-nuclear discourse has affected Japan’s disarmament policy throughout the post war period until now. Japan faced security challenges in the 1960s and the 1970s, but it chose not to go nuclear. Behind such a decision, there were strategic considerations on pros and cons of the nuclear option. The Japanese society also had a nuclear taboo, which was shaped with experiences of Hiroshima, Nagasaki and Daigo Fukuryu Maru, and has influenced the public policy discourse. This dilemma further deepened as a movement for the legal ban of nuclear weapons based on considerations of the humanitarian consequences of nuclear weapons was intensified, while the security environment in East Asia requires Japan to under the US security commitment of extended nuclear deterrence.