To supply oil with certainly and optimum efficiency with small-sized or medium-sized pumps to a large sized engine by feeding or passing pump medium in the same direction as the rotation of a drive shaft of a controllable pump.

A controllable pump 1 has a drive shaft 10 commonly used by a constant displacement pump 2. The constant displacement pump 2 is operated for discharging a constant amount of lubricating oil, while the discharge amount of the controllable pump 1 is dependent on pressure at a discharge port 6 or a system 8 to be supplied. A discharge port 7 of the constant displacement pump 2 is branched. One of the branched port is communicated with the system 8 to be supplied through a check valve 3, while the other is returned to an oil tank 5 though a second valve 4. The check valve 3 opened to a pumping direction of the constant displacement pump 2 is previously pulled in a closing direction, accordingly. On the other hand, the valve 4 for the return to the oil tank 5 is previously pulled in an opening direction, or operated based on a float vertically moved in accordance with the oil level.