Software is a prominent factor of infrastructure in a modern information society. However failures in software development project such as cost or deadline over still remain. One of causes of the failures is considered a lack of postmortem analysis for project improvement. Because a postmortem analysis has high costs of time and human resource, it is difficult to perform the analysis continuously under the current circumstances. In this research, we focus on email conversations often used in software development, and we propose a method for visualizing them in the project. Our method helps to grasp "contexts" in development further to existing visualizing approaches such as metrics chart that can reveal only "state". In this paper, we describe details of our method and case studies of applying the method to actual projects.