PURPOSE: To surely feed oil to oil fed sections at all times by adjusting the amount of stored oil of an air hydraulic oil converting means by the use of oil circulated from an oil receiving means.

CONSTITUTION: In order that not only a feed side air hydraulic oil converter 10 functions as a receiving means of oil O at all times, but also a receiving side air hydraulic conveter 20 functions as a receiving means of oil O at all times, oil O in the feed side air hydraulic oil 10 is gradually decreased following the telescopic motion of each hydraulic cylinder actuator 100, 200, 300 and 400, and oil O in the receiving side air hydraulic oil converter 20 is gradually increased by the amount of oil decreased on the contrary. Thus as mentioned above, the amount of stored oil in each air hydraulic oil converter 10 and 20 is monitored by beam sensors 16 and 26 at all times, and since oil O in the receiving side air hydraulic oil converter 20 is so designed as to be circulated to the feed side air hydraulic oil converter 10 when the amount of storage oil reaches a value specified in advance, oil is surely fed to the hydraulic cylinder actuators 100, 200, 300 and 400 at all times.