This is an STS case study of the social decision-making process on the siting of a nuclear power plant in Japan, from the point of view of a sociological case analysis. Energy technologies are critically important for industrial society but often trigger serious disputes through the R&D phase and the phase involving introduction into society. Nuclear power technology especially has provoked a lot of conflicts all over the world. By focusing on serious trust issues among decision-making processes and stakeholders, we found very interesting consequences and/or results of participatory social decision-making process in nuclear issues. As an example, we take up the case of a local referendum in the siting area (Maki-machi town, Niigata prefecture of Japan) and describe and analyze it to highlight the critical sociological factors involved in the application of participatory methods in social decisionmaking processes regarding technological issues. Through this description and analysis, we would like to emphasize the effects of the complicated and subtle structure of local context on the consequence of local decision-making processes. We then propose a concept, "relevant marginal actor," to clarify which actors play critical roles in the whole local decision-making process in which controversial technological issues are framed, and reframed.