In the first valve group of the hydraulic valve device 12, in order to smoothly raise the boom in the three combined operation of the boom up, the arm cloud, and the bucket cloud in the pressure relief device of the hydraulic excavator, The secondary pressure C as the operation command for the boosting operation is introduced to the pilot operating portion 70a of the load check valve 70 of the feeder passage 32 of the direction changing valve 21 via the line 71 The variable throttle valve 70 is fully closed when the secondary pressure C is zero or less and the opening area of the variable throttle valve 70 is reduced as the secondary pressure C is great, ) Of the pressurized oil.
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