Hydraulic control circuit for working machine

A hydraulic control circuit for a working machine, the hydraulic control circuit comprising:

• a hydraulic pump of variable displacement type;
• a hydraulic actuator driven by the hydraulic pump as a hydraulic supply source;
• a control valve for performing oil supply/discharge controls to/from the hydraulic actuator on the basis of an operation of an operation lever;
• a bypass oil passage formed by being branched from a discharge line of the hydraulic pump and extending to an oil tank;
• a bypass valve having a variable opening area for controlling a flow rate of the bypass oil passage;
• and
• a controller for controlling a displacement varying means of the hydraulic pump and the bypass valve,
• wherein the controller,
• performs closed-loop control for maintaining a pump flow rate constant, and controlling an opening area. of the bypass valve so that a pump pressure is maintained at a set pressure, during non-operation of the operation lever, and on the other hand,
• performs open-loop control for increasing the pump flow rate depending on the operation input of the operation lever, and reducing an opening area of the bypass valve depending on the operation input of the operation lever, during operation of the operation lever, and
• wherein the controller comprises a correcting means for correcting a correspondence relationship between the operation input of the operation lever and the opening area of the bypass valve in the open-loop control, on the basis of the opening area of the bypass valve during the closed-loop control.