P1 moves on vertical smooth surface with holing the body on the surface using one suction cup. Two wheels are independently driven by stepping motors. In this mechanism, the most important point is the ratio of friction forces of suction cup and tire. High friction between the tire and the surface of window transmits the torque, and low friction between the suction cup and the surface of window achieves to move the robot with holding the body on the window. We selected PTFE (Polytetrafluoroethylene) for the materials of surface of a suction cup, and silicon rubber for the material of tires.