This paper aims at finding the answer to the essential question: Can people perceive a robot's presence as having a social existence? We attempt to apply a sociological and psychological approach to understand the influence of robot beings, by observing human emotion and perception changes while subjects watched a funny video clip in the presence of a robot or a human companion, each of which made their own typical laughing sounds. From this experiment, we found that the robot did not affect the human's positive emotions as much as a human companion did, but the robot did discourage negative emotions. However, the subjects were, in general, amused when they were watching the video with the robot. This amusement is similar to the contagious effect of sharing humor with another human being. Our findings suggest that the subjects accepted the robot's presence as a kind of existence empathically.