PURPOSE: To prevent the shortage of assist even in a sudden steering by reducing the discharge by a PS pump as the speed of a car is increased and controlling it to be increased as the rotational speed of a steering wheel is increased.

CONSTITUTION: A discharge control valve 19 is provided on the way of a pipe 15 to supply the fluid generated by a PS pump 14 driven by an engine 18 to a PS-operation cylinder 11. The discharge control valve 19 is controlled by a controller 30 to reduce the discharge as the car speed is increased and increase the discharge as the steering speed of a handle is made greater and more sudden on the basis of signal from a car speed sensor 22. This construction permits to obtain a speed-sensing type PS without causing the shortage of assist of PS when a handle is suddenly operated.