A hydraulic operation controlling unit where the engine can be driven stably at a target output torque point and reduction in the work speed can be prevented at the time of light load, includes an engine control unit controlling the output of an engine, so that the output properties of the engine become equi-horsepower properties or approximately equi-horsepower properties in a predetermined engine speed range (N.sub.2 to N.sub.6) that includes engine speed N.sub.3, which corresponds to a matching point M.sub.3. A controlling unit increases or reduces the absorbing torque of a hydraulic pump in response to an increase or decrease in the engine speed, and thus, controls the absorbing torque of the hydraulic pump so as to make the output torque T.sub.3 of the engine, which corresponds to matching point M.sub.3, and the absorbing torque of the hydraulic pump coincide with each other.