PURPOSE: To provide a constant steering reaction in the backing up of a vehicle by providing a reaction adjusting valve in a path affording communication between a pair of reaction chambers of a control valve to controllably open and close said valve according to signals from a back-up switch and a vehicle speed sensor.

CONSTITUTION: A pair of reaction chambers 43, 44 are provided at both sides of a spool 31 of a control valve 13 and communicates with each other through a reaction communicating path 15. A reaction adjusting valve 16 is provided in the reaction communicating path 15 and controlled by a control unit 60 on the basis of signals from a back-up switch 61 and a vehicle speed sensor 62 with respect to the throttle. That is, the reaction adjusting valve 16 is controlled such that in low speed travelling the throttle amount of said valve 16 is small and in the high speed travelling the throttle amount is large. Further, in the backing up of vehicle a constant throttle amount of the reaction adjusting valve 16 is provided.