A hydraulic drive system for a civil engineering and construction machine of the present invention comprises a hydraulic pump (11, 11A), a plurality of actuators (4-6) driven by a hydraulic fluid supplied from the hydraulic pump and including an arm cylinder (5) and a boom cylinder (4), a plurality of flow control valves (12, 14, 16) for controlling flows of the hydraulic fluid supplied to the respective actuators and including an arm directional control valve (14) and a boom directional control valve (12) and a plurality of distribution compensating valves (13, 15, 17; 13A, 15A, 17A) for controlling differential pressures across the respective flow control valves, the distribution compensating valves each having a first device (13d,15d, 17d; 13e, 13f, 15e, 15f, 17e, 17f) to set a target value of the differential pressure across the associated flow control valve. The present invention is featured in further comprising a first device (21) for detecting an arm crowding operation performed by driving of the arm cylinder (5), and a second device (24, 30, 31; 24, 30A, 31) for controlling the drive means (15d; 15f) of the distribution compensating valve (15; 15A) associated with the arm cylinder so as to reduce at least the target value of the differential pressure across the flow control valve (14) associated with the arm cylinder, when the arm crowding operation is detected.