CONSTRUCTION MACHINE

摘要

Provided is a construction machine capable of both of cavitation prevention and reduction in a power loss. The construction machine includes: a lower traveling body; an upper slewing body; a front attachment; a plurality of hydraulic actuators including traveling motors (13 and 14); hydraulic pumps (10 and 11); a plurality of control valves (16 to 21) for the hydraulic actuators; a plurality of operation units (22 to 27) for the control valves (16 to 21); traveling operation detectors (38 and 39) that detect operations for the operation units (25 and 26) for the traveling motors of the operation units; a back-pressure compensation valve (29) generating back pressure in a return pipe line (28) connecting each of the control valves and a tank and having a setting pressure switchable between low and high pressure setting values; and a back-pressure control section (31 and 32) performing a back-pressure lowering control of making the setting pressure of the back-pressure compensation valve (29) be the low pressure setting value when traveling operation amounts in the traveling operation units are large.