1. An apparatus for a learning emotion of a robot, comprising: an internal state calculation unit configured to detect external environment information and calculate an internal state vector value, corresponding to one point of an internal state coordinate system, based on the detected external environment information; an emotion decision processing unit configured to generate an emotion value within each emotion value group, indicated by coordinates of an internal state input value of the robot on the internal state coordinate system, as an emotion of the robot; a behavior generation unit configured to decide a behavior of the robot based on the emotion value decided by the emotion decision processing unit and make an emotional expression based on the decided behavior; and an emotion learning unit configured to generate feedback information on the emotion value, corresponding to one point of the internal state coordinate system, based on the emotion value decided by the emotion decision processing unit and information on a type of emotion received from a user input unit and change an emotion probability distribution of the internal state coordinate system using the feedback information.