Behavior synchronization of humans during conversation and cooperative task has been studied in psychology. In robotics, several researchers also have been studying cooperative task between a human and a robot referring to these studies. However, mechanisms of behavior synchronization are still unclear because of complexity of human being. Therefore, referring to animal psychology, we propose a novel experimental methodology to study behavior synchronization through interaction experiments between a rat and a robot. We then developed small mobile robots and an experimental setup. This experimental setup consists of two open-fields. A robot and a rat are released into each open-field. The robot reproduces motion of the rat in the other open-field. Using this experimental setup we also performed a preliminary experiment to investigate behavior synchronization. In this paper, we describe the robot and the experimental setup. We also introduce result of the experiment briefly.