CUT-OFF DEVICE FOR HYDRAULIC PUMP

PROBLEM TO BE SOLVED: To enable energy saving operation without complicated operation by detecting an operation condition of at least one of plural operation means, and changing a responsive characteristic to a level to decrease the discharge flow amount of a hydraulic pump to a cut-off flow amount. SOLUTION: A hydraulic driving device provided for a hydraulic shovel comprises operation lever devices 12-18 for operating hydraulic cylinders 5, 6, 8 and hydraulic motors 9-11, respectively, and regulators 19, 20 for controlling a pushed-aside volume of each hydraulic pump 1, 2. A cut-off device is also provided to operate the regulators 19, 20 so as to reduce the discharge flow amount detected by the pressure sensors 56, 58 to a specified cut-off flow amount under a cut-off pressure in the vicinity of a maximum pressure determined by a relief valve 4. This cut-off device is constructed so as to change its response characteristic to reduce the discharge flow amount to the cut-off flow amount according an operation detection signal of each operation lever devices 12-18.