In this paper, we develop a virtual experimental environment to investigate users’ eye gaze in human-robot social interaction, and verify it’s potential for further studies. The system consists of a 3D robot character capable of hosting simple interactions with a user, and a gaze processing module recording which body part of the robot character, such as eyes, mouth or arms, the user is looking at, regardless of whether the robot is stationary or moving. To verify that the results acquired on this virtual environment are aligned with those of physically existing robots, we performed robot-guided quiz sessions with 120 participants and compared the participants’ gaze patterns with those in previous works. The results included the followings. First, when interacting with the robot character, the user's gaze pattern showed similar statistics as the conversations between humans. Second, an animated mouth of the robot character received longer attention compared to the stationary one. Third, nonverbal interactions such as leakage cues were also effective in the interaction with the robot character, and the correct answer ratios of the cued groups were higher. Finally, gender differences in the users’ gaze were observed, especially in the frequency of the mutual gaze.