PURPOSE: To achieve high precise control excellent in controlling properties by using returned oil, while the size-reducing and the cost-lowering of whole device are contrived.
CONSTITUTION: While a plurality of hydraulic actuators Ma, Mb are driven by one hydraulic pump 2, the oil returned from the hydraulic actuators Ma, Mb is fed directly to the hydraulic pump 2. Then, while the by-pass circuit 5 which uses the control valve such as a check valve 5c, etc., returning a part of returning oil to an oil tank 4 is connected to the part between the returning line 3 from the hydraulic actuators Ma, Mb and the oil tank 4, a semi close hydraulic circuit 7 is provided, and said hydraulic circuit is made by connecting the interference-preventing circuit 6 using a check valve into the returning line 3a from the hydraulic actuator Ma in which feeding oil-amount is different from discharging oil-amount.
NAKAMURA NOBUYUKI
KODA NORIHIRO
