E-mail discussions are often conducted during intellectually challenging activities such as research, cooperative learning, and software development. It is important but generally difficult to successfully grasp the processes of the discussions and their conclusions since a mass of e-mails is accumulated in e-mail applications. Furthermore, actual e-mail discussions contain descriptions of diverse sizes. These features hinder grasping the discussion processes. Although some research projects have aimed at extracting discussion processes, these existing methods have not considered the diversity of description granularity. Therefore, our research is intended to develop methods for extracting the discussion processes and a system for visualizing the discussion processes. This paper mainly describes a system for visualizing discussion processes in a mass of e-mails. Initially, this paper describes the system design based on a study of the features of actual e-mail discussions. This paper also describes the development of a prototype.