Patent ID: 8521374

Claim:
A hydraulic working machine provided with a hydraulic pump as a main pump, a variable displacement hydraulic motor actuated as a travel motor by pressure oil delivered from the main pump to allow a travel base to travel, a traveling directional control valve for controlling a flow of pressure oil to be fed from the main pump to the travel motor, a traveling control device for switchingly controlling the traveling directional control valve, a travel speed control unit for controlling a tilt angle of the travel motor in such a state that the travel motor revolves at one of two speeds consisting of a low speed and a high speed, and a boost control unit for controlling a maximum delivery pressure of the main pump, said travel speed control unit being provided with a hydraulically-actuated, traveling tilt-angle control device for controlling the tilt angle of the travel motor, a travel speed selector part operably arranged to instruct selection of one of the low speed and high speed, and a traveling, hydraulic pressure oil feed part operably arranged to control hydraulic pressure oil, which is to be fed to the traveling tilt-angle control device, based on an instruction from the travel speed selector part, and said boost control unit being provided with a hydraulically-actuated, relief pressure control part operably arranged to control a preset relief pressure at which the maximum delivery pressure of the main pump is to be regulated, a boost-pressure switching selector part operably arranged to instruct to select, as the preset relief pressure of the relief pressure control part, one of a normal-time relief pressure and a boost-time relief pressure which is a pressure higher than the normal-time relief pressure, and a boosting, hydraulic pressure oil feed part operably arranged to control hydraulic pressure oil, which is to be fed to the relief pressure control part, based on an instruction from the boost-pressure switching selector part, characterized in that: the hydraulic working machine is provided with only a single hydraulic pressure oil feed part commonly usable as the traveling, hydraulic pressure oil feed part of the travel speed control unit and also as the boosting, hydraulic pressure oil feed part of the boost control unit.