In recent years, the power conversion using oil pressure attracts attention as measures against global environment problems. Although a hydraulic motor is effective in oil pressure-power conversion, this is designed for high pressures such as several 10 MPa. So apparatus suitable for the oil pressure-power conversion of low-pressure is needed from now on. Authors made the property evaluation equipment for the power recovery which built into the closed circuit used a slanting axis type hydraulic pump/motor, and performed evaluation examination about the power recovery from the circulating oil of several MPa.