The“black rain”survivors’movement has been spearheaded by the “Hiroshima Prefecture Black Rain’Survivors’Liaison Conference”(or“Renraku-kyo”) since its formation in November 1978. In November 2015, the Conference initiated a class-action lawsuit against the government in the Hiroshima District Court for the issuance of Atomic Bomb Survivor Certificates and Class 1 Health Check Certificates. The present article discusses the activities in terms of social movement, chiefly drawing upon Alberto Melucci’s (1943-2001) theory of social movement with a special emphasis on the creation and transformation of the collective identity of the participants in the movement. Finally, this paper will discuss the establishment of collective identity as one by-product of the movement.