Risshō Kōsei Kai (立正佼成会; until June 1960, 大日本立正交成会: Dai-Nippon Risshō Kōsei Kai?) is a Japanese new religious movement founded in 1938 by Nikkyo Niwano and Myoko Naganuma. Rissho Kosei Kai is organized as a lay Buddhist movement, which branched off from the older Reiyukai, and is primarily focused around the Lotus Sutra and veneration of ancestors.
Rissho Kosei-kai was founded on March 5, 1938 by Nikkyo Niwano and Myoko Naganuma, both former members of the Buddhist sect Reiyūkai. Rev. Niwano met Ms. Naganuma while he was engaged in missionary work with Reiyukai and the two became close friends. In 1938, they attended a Reiyukai meeting in which its president made remarks that lectures and study of the Lotus Sutra were out of date. After hearing that and consulting with each other, they determined that they could not support such ideas and left Reiyukai. It was then that they decided to form a new organization. The first meeting was held at Mr. Niwano's house and some 30 people joined at that time.
The organization grew quickly, and by 1941, membership had reached 1,000. For a short period between 1949 and 1950, Rissho Kosei-kai served as a lay auxiliary organisation of Nichiren Shū, but Niwano could not stem what he considered to be the liberal policies of Nichiren Shū. No longer able to meet at Rev. Niwano's house, construction on a new headquarters began. However, as membership continued to grow the new headquarters also became too small and work on the Great Sacred Hall, or daiseidō (大聖堂?), began in the late 1950s'. Myoko Naganuma, who had been serving as Vice-President, died before the Great Sacred Hall was completed, dying on September 10, 1957. Seven years later, it would be completed.