PURPOSE: To improve the stability of a hydraulic servo system by providing a gain control resistance, a temperature compensation thermistor and a phase compensation coil between a velocity transducer and an auxiliary coil.

CONSTITUTION: A velocity transducer 23 and an auxiliary coil 5 are connected to each other via a pressure feedback circuit 24 having a temperature compensation thermistor 26, a gain control resistance 27 and a phase compensation coil 25, thereby an electrical hydraulic servo valve 3 is controlled, such as negating the differential variation generated by external disturbance or the line and since it is controlled stably under the wide range temperature environment, the stability of a hydraulic servo system is improved.