Recently, application of robotics to prostheses has been studied. To improve operability of prostheses, an embodiment of prostheses is important. The purpose of this research is embodiment of extra robotic thumb. We have developed a robotic thumb and a manipulation interface. The artificial thumb is almost same size as a human thumb and is attached on a palm of the left hand. We operate the artificial thumb by an interface equipped with right hand. We performed some experiments to evaluate effect of sensory feedback and found that sensory feedback improves an operability and emobodiment of the prostheses.