PURPOSE: To make variations in steering force small in order to carry out safe steering operation, by supplying oil at a predetermined flow rate into a power steering device when zero drive current is fed to an electrically driven control valve.

CONSTITUTION: The flow rate of oil which is controlled by a solenoid valve 9 is actually controlled by a solenoid 9a when the speed of a vehicle is below a value V0, but is controlled when the speed is above the value V0, and decreases homogenously as the vehicle speed increases. When a drive current circuit fails and therefore no drive current is fed to both solenoids 9a, 9, the flow rates is fixed corresponding to the value V0 irrespective of the vehicle speed.