In recent years, the situation surrounding social infrastructure development has changed drastically, and Civil Engineering Consulting Firms are accordingly required to expand and diversify the scope of activities. The purpose of this study is, with an eye on the early-stage Social Acceptability that could be one of the factors causing delay and inhibition in geothermal development process, in the development of renewable energies for the realization of a decarbonized society, to examine the application of such project management methods, that have already been established and thus generally utilized in the construction management area, into a process of consensus building as a method that contributes to the solution of the problems. More specifically, the activity policy in reference to the project stakeholder management based on the PMBOK is proposed, and then a systematic implementation method of consensus building activities, consisting of eight stages and three systems is presented, based upon the verification result of implementing multi-year projects in practice. This study proposes versatile and systematic activity methods in future geothermal development field.