Robotics is contributing to studies on animal behavior. Mobile robots are actually used as devices to give external stimulus to animals in several experiments. We consider that this approach can be applied to studies in psychic medicine. In psychic medicine, all new drugs are evaluated in experiments using animal models of mental disorder before using it in clinical practice. However, conventional animal models have some problems in the construct validity. The animal models should be developed through the method which is consistently associated with the theory of the mental disorders while many of conventional models had been developed by genetic manipulations or surgical operations on nerve system. We considered that a novel animal model could be developed by stress exposure using a small mobile robot. We then implemented this method to the experimental system which had been developed in our past study. An experiment was conducted using the system, and the method was then verified. Therefore, we conclude that the animal model of depression developed by proposed method, exposing continuous attack by the robot in immature period and interactive attack in mature period, can be a novel animal model of depression.