With the recent developments in fields like Artificial Intelligence and Robotics, the rise of social robots is not far away. For social robots to establish better human interaction, they must be able to interact with people casually. In this research, we introduce the idea of empathy in robots by syncing our emotions with the robot’s facial expression. The emotions are estimated and synchronized in real-time using biological signals (i.e., brainwave and heartrate). In this paper, we (1) investigate the effect that emotion synchronization has in human-robot interactions by comparing the impressions of a robot that generates synchronized facial expressions with non-synchronized ones, and (2) clarify the effectiveness of selecting stimulus according to the individual’s interest. The results suggest that emotion synchronization of facial expressions is an effective way to improve human-robot interactions.