1. An apparatus for a robot capable of learning emotion, the apparatus 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 a set of emotion values 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 set of emotion values decided by the emotion decision processing unit and make an emotional expression based on the decided behavior by performing a facial expression processing or a voice output processing of the robot, in which the robot comprises an emotional expression organ including at least one of a mouth, an eye, a head, an arm, a leg, and a body; and an emotion learning unit configured to generate feedback information regarding the set of emotion values, wherein the set of emotion values corresponds to one point of the internal state coordinate system, based on the set of emotion values decided by the emotion decision processing unit and information regarding a type of emotion received from a user input unit and configured to change an emotion probability distribution of the internal state coordinate system using the feedback information, wherein the emotion probability distribution comprises a first plurality of Gaussian distributions, each having weight, a central value, and a variance, or a second Gaussian distribution comprising the first plurality of Gaussian distributions, and wherein the emotion learning unit is configured to retrieve a Gaussian distribution corresponding to the feedback information using a matching function and is configured to change the Gaussian distribution of the emotion probability distribution based on the retrieved Gaussian distribution.