The authors have been studying the Pendulor type energy converter with some excellent merits : -simple, highly efficient, safe and so on, for eight years. This paper deals with the absorbing efficiency of the wave converter affected by the system's elasticity which depends on the deformation of the power members and the compressibility of oil in the power cylinder. The authors investigated the behavior of the elasticity during the operation and explicated the relationship between the efficiency and the elasticity. The deformation by the elasticity and the compressibility reduces the efficiency, as the load ratio increases. To improve this insufficiency effect, appropriate measures are needed. According to these results, several methods for improving the efficiency, including the Pendulor's hydraulic circuit and its components, were introduced.