The goal of our research is to clarify factors that are necessary for coexistence between human and robot. However, evaluating communications between humans and robots is quite difficult due to the existence of several uncertain factors that exist in human communication and variety of personalities. Therefore, as a first step, a more previous species, rats were selected. We conducted interactive experiments between rats and robots. We investigate basic factors that are necessary for symbiotic relationship between living creatures and robots. To conduct such experiments, we developed a new rat-robot (WM-6) and experiment systems. Three experiments have been conducted: "calling robot", "recognizing behavior", and "choosing reward". The results of these experiments show that we succeeded in making a rat to act on the robot by itself. Moreover, the rat could recognize two behavioral patterns of the robot ("translation" and "rotation"). Finally, the rat could change its interaction with the robot based on its need. Consequently, we succeeded in creating various interactions between rat and robot.