PURPOSE: To change the reaction pressure applied to a steering wheel shaft from the hydraulic device of a servo steering device in response to the vehicle speed, at the time of turning operation of the vehicle.

CONSTITUTION: A main valve mechanism comprises a pair of parallel fluid circuits equipped with throttles 1, 2 and 1', 2', and produces an assistance pressure Pa to be applied to a hydraulic assistance device 12; and an auxiliary valve mechanism comprises a pair of parallel fluid circuits equipped with throttles 3, 4 and 3', 4' and produces a reaction pressure to be applied to a steering wheel shaft. A first pressurizing fluid source supplies a definite flow-rate of fluid to the main valve mechanism, and a second pressurizing fluid source supplies a variable flow-rate of fluid to the auxiliary valve mechanism by the pump being driven in response to the wheel speed, so that the reaction pressure can be correspondingly made variable.