Recent 3D graphics hardware technologies have made it possible to create visually realistic 3D characters and 3D scenes in real time. And then, the video game has become one of the main applications of 3D graphics technologies. However, behaviors of Non Player Characters (NPCs) in video games are not satisfactory because they are still predefined and then very simple. To attract game players, NPCs should have more complicated behaviors like the human. Facial expression is one of the most important factors for such a humanlike NPC. In this paper, the authors propose an NPC which interacts with the human. The NPC changes its facial expression according to its emotion during the interaction. For realizing such an NPC, the authors implemented a neural network based emotional model unit . By some experiments, this paper also shows that the NPC can change its facial expression according to its emotion like the human.