In this paper, the authors make a hypothesis of a factor model to stimulate student group work and examine the model by conducting questionnaire surveys of undergraduate students who participated in a year-long project-based learning at the Scool of Network and Information, Senshu University. 511 students answered two surveys on their experience and feelings in the middle of and in the end of their project-based learning. Our findings are as follows: (a) some portions of our initial model are supported, (b) positive atmosphere in a group and good task management stimulate group learning activities. The results indicate that students should make opportunities to have convivial meetings and share recreational activities at astage in the formation of their groups. Furthermore, task management is an important element to stimulate their group work in the period of promoting their learning activities.