Japan’s refusal of belligerence is a key element of its constitution of 1947, in which the country explicitly revokes the right to wage war. On this basis, in the past the role of Japan's military was interpreted as purely defensive in nature. However, it has remained unclear whether Japan's Self-Defense Forces (SDF) were allowed to join efforts of collevtive security under United Nations guidance. The paper discusses this issue on two fields: Firstly, how can Japan contribute to achieving a global peace based on order ans justice? Secondly, and alternatively does Japan need to abandon the ideal of a peaceful world and, correspondingly, need to revise its constitution?