McKibben type artificial rubber muscle has high affinity with human body due to mechanical flexibility and light-weight. It is widely used for personal care robots as the reason for above. Therefore, several models of artificial muscle based on energy conservation law to control the artificial muscle had been proposed in previous studies. However, parameters in the previous study are determined from trial-and-error to decrease the modeling error, but these determined parameters do not necessarily show the actual values of physical property of material. Purpose of this study is to construct a model from which the characteristic of McKibben type artificial muscle can be calculated based on only design parameters and actual rubber physical property. In this paper, first of all we propose expansion plane model to consider balance state of several forces. Subsequently, elastic force owing to rubber material is modeled based on Mooney-Rivlin model. And then the precision of proposed model is confirmed experimentally.