To provide a hydraulic drive servo system capable of realizing both of slow speed and highly accurate servo control for accurate machining and rapid feed control for reducing cycle time.

A movable cylinder 10-1 in a cylinder mechanism 10 is hydraulically driven to drive a driven body connected there to This circuit includes a first hydraulic circuit for performing the driven feed body accurate feed motion in a low speed range through a small capacity servo valve 11 capable of changing over a drive direction normally and revesely and a second hydraulic circuit for performing the driven body motion in a high speed range including a first valve means comprising large capacity valves 15 and 16 for normal drive direction and a second valve means comprising large capacity valves 17 and 18 for reverse drive direction. The circuit is connected the first and second hydraulic circuits being parallel with each other between a hydraulic pressure source and the cylinder mechanism and provided with a controller 20, which controls the first and second valve means and a servo valve according to the signals, position commands PC and speed commands SC sent form a position detecting sensor 19.