Kōfuku no Kagaku (Happy Science) represents one of the most visible and institutionally complex New Religious Movements (NRMs) to emerge in late twentieth-century Japan. Founded in 1986 by Ōkawa Ryūhō, the movement presents itself as a universal spiritual system that integrates elements of Buddhism, modern metaphysics, and global religious traditions into a unified doctrinal framework. Central to its teachings is a highly developed cosmology, including multi-dimensional spiritual worlds, reincarnation theory, and the worship of a supreme divine entity known as El Cantare.The primary research problem addressed in this monograph is how Kōfuku no Kagaku constructs religious authority and cosmological legitimacy in a modern context characterized by scientific rationalism, globalized spirituality, and religious pluralism. In particular, the study examines how the movement reconciles claims of supernatural revelation with modern discourses of knowledge, progress, and institutional credibility.The aim of this work is threefold. First, it seeks to reconstruct the historical and intellectual development of Kōfuku no Kagaku, situating it within the broader postwar Japanese religious landscape. Second, it analyzes the movement's doctrinal system and cosmological structure as internally coherent symbolic systems. Third, it evaluates the sociological implications of its institutional expansion, media strategies, and global utopian ideology.Rather than treating the movement solely as an object of belief or critique, this study approaches it as a complex cultural and religious system that reflects broader transformations in contemporary spirituality.