Minorities are typically deprived of social resources. To survive in such a harsh environment, they often organize mutual aid associations. As an example of one such association, the rotating credit association of migrants was investigated for three purposes: the first, is to examine the function of a rotating credit association upon the economic adaptation. The second is to examine the components of a rotating credit association which induce cooperative behavior through generalized exchange. The third is to reveal the qualifications for membership into a rotating credit association. For these purposes, 30 Japanese migrants were interviewed. The conclusions were as follows: the effectiveness to advance the economic adaptation was contingent on economic circumstances. The institutions make it possible for members to cooperate with others for their own self-interest. Altruistic motives are not necessarily required. The qualification for affiliation with the association was determined not by ethnicity but by personal relationships.