The authors have been developing human-like head robots in order to develop new head mechanisms and functions for a humanoid robot that has the ability to communicate naturally with a human by expressing human-like emotion. When humans communicate through auditory or visual sensations, they estimate their mental state through not only the information of each sensation but also their mental model. A robot's mental model consists of a 3D mental apace having a pleasantness, an activation and a certainty axes. When the robot senses the stimulus, a mental vector moves in this mental space based on the Equations of Emotion. We also proposed a Robot Personality, which consists of the Sensing Personality and the Expression Personality. Further, we assigned and loaded various Sensing Personalities.