McKibben pneumatic actuator has good characteristics for an actuator of a robot. For this reason, McKibben pneumatic actuator has come to be used for actuators of the robot. Then it is well known that the robot driven by McKibben pneumatic actuator generates a stable motion in spite of a simple control. However, it was not discussed enough how the characteristic of McKibben pneumatic actuator acted on the stability of robot's motion. Then in our previous research, the physical model of McKibben pneumatic actuators was improved and discussed the stability of the robot position using the model. In this paper, the validity of this model used in the analysis of previous studies is evaluated through some experiments.