In the domain of psychology and medical science, many experiments have been conducted referring to research on animal behaviors, to study the mechanism of mental disorders and to develop psychotropic drugs to treat them. Rodents such as rats are often chosen as experimental subjects in these experiments. However, according to some researchers, the experiments on social interactions using animals are poorly- reproducible. Therefore, we consider that the reproducibility of these experiments can be improved by using a robotic agent that interacts with an animal subject. We have developed a novel quadruped rat-inspired robot, the WR-2 (Waseda Rat No.2), based on the dimension and body structure of a mature rat. It is capable of reproducing the behaviors such as walking, mounting, rearing and grooming of the rat.