A control system for a hydraulic construction machine comprising: a prime mover; at least one variable displacement hydraulic pump (1, 2) driven by said prime mover; at least one hydraulic actuator driven by a hydraulic fluid from said hydraulic pump; input means for commanding a reference target revolution speed of said prime mover; revolution speed control means for controlling a revolution speed of said prime mover; and operation command means for commanding operation of said hydraulic actuator, wherein said control system comprises: target revolution speed setting means (70, 700a-700v) for setting a target revolution speed of said revolution speed control means based on the reference target revolution speed; operation detecting means (73, 74, 77-81) for detecting a command input from said operation command means; and load pressure detecting means (75, 76) for detecting a load pressure of said hydraulic pump, and wherein said target revolution speed setting means comprises: a first modifying section (700d1-700d6) for changing the target revolution speed depending on the command input from said operation command means, which is detected by said operation detecting means; wherein said target revolution speed setting means further comprises: a second modifying section (700v, 700g) for modifying change of the target revolution speed, which is given by said first modifying section, depending on the load pressure detected by said load pressure detecting means, wherein said second modifying section (700v, 700g) modifies the change of the target revolution speed, which is given by said first modifying section (700d1-700d6), to be a minimum when the load pressure detected by said load pressure detecting means (75, 76) is lower than a first value, characterized in that said first modifying section includes first means (700d1-700d6) for computing a first revolution speed modification value corresponding to the operation input from said operation command means, which is detected by said operation detecting means (73, 74, 77-81), said second modifying section includes second means for computing a second revolution speed modification value (DNLR) corresponding to the magnitude of the load pressure detected by said load detecting means, and third means for executing computation based on the first revolution speed modification value and the second revolution speed modification value, to thereby obtain a third revolution speed modification value, and said first and second modifying sections further include fourth means for executing computation based on the third revolution speed modification value and the reference target revolution speed, to thereby obtain the target revolution speed. a prime mover; at least one variable displacement hydraulic pump (1, 2) driven by said prime mover; at least one hydraulic actuator driven by a hydraulic fluid from said hydraulic pump; input means for commanding a reference target revolution speed of said prime mover; revolution speed control means for controlling a revolution speed of said prime mover; and operation command means for commanding operation of said hydraulic actuator, wherein said control system comprises: target revolution speed setting means (70, 700a-700v) for setting a target revolution speed of said revolution speed control means based on the reference target revolution speed; operation detecting means (73, 74, 77-81) for detecting a command input from said operation command means; and load pressure detecting means (75, 76) for detecting a load pressure of said hydraulic pump, and target revolution speed setting means (70, 700a-700v) for setting a target revolution speed of said revolution speed control means based on the reference target revolution speed; operation detecting means (73, 74, 77-81) for detecting a command input from said operation command means; and load pressure detecting means (75, 76) for detecting a load pressure of said hydraulic pump, and wherein said target revolution speed setting means comprises: a first modifying section (700d1-700d6) for changing the target revolution speed depending on the command input from said operation command means, which is detected by said operation detecting means; a first modifying section (700d1-700d6) for changing the target revolution speed depending on the command input from said operation command means, which is detected by said operation detecting means; a second modifying section (700v, 700g) for modifying change of the target revolution speed, which is given by said first modifying section, depending on the load pressure detected by said load pressure detecting means, wherein said second modifying section (700v, 700g) modifies the change of the target revolution speed, which is given by said first modifying section (700d1-700d6), to be a minimum when the load pressure detected by said load pressure detecting means (75, 76) is lower than a first value,