Patent ID: 7594395

Claim:
A hydraulic control device for a working machine comprising: control valves switched by operating means; hydraulic actuators separately controlled by corresponding control valves, the hydraulic actuators and the control valves being divided into two groups consisting of the first and the second groups, oil discharged from common hydraulic pumps being supplied to both of the two groups; unified bleed-off valves separately performing unified bleed-off operation on all of the control valves belonging to each of the first and the second groups on the basis of signals output from controlling means according to inputs from the operating means; central bypass paths provided in the control valves, the central bypass paths of the each group being connected in tandem so as to form a central bypass line for unloading operation; and bypass-cutting valves disposed adjacent to the most downstream part of the central bypass lines for opening or closing the central bypass lines, wherein the bypass-cutting valves are automatically switched on the basis of the signals output from the controlling means, and are adapted to open the central bypass lines when the unified bleed-off valves are not operated.