HYDRAULIC DRIVE DEVICE FOR WORK MACHINE

To provide a hydraulic drive device for a work machine that is capable of ensuring reduction in fuel consumption even in actual work where an operating condition changes every moment. Operating condition identifying unit (41) for identifying the operating condition and hydraulic pump control system (40b) for controlling absorption torque of hydraulic pump (18) are provided. When the operating condition identified by operating condition identifying unit (41) is a specific operating condition, hydraulic pump control system (40b) controls the absorption torque of hydraulic pump (18) to achieve hydraulic pump absorption torque characteristic line (PLb) matching the absorption torque of hydraulic pump (18) with output torque of engine (17) at engine output torque point Mb at which a fuel consumption rate is substantially minimum.