PURPOSE: To make a power-assisted quantity possible to be set up at will, by installing a power-assisted quantity variable setter at the input side of a control element belong to a power steering unit in which the power-assisted quantity varies according to car speed and the steering speed of a steering wheel.

CONSTITUTION: A discharge rate of an electric-powered oil pump 4 is controlled by a driving signal out of a controller 8 to be varied according to car speed and the steering speed of a steering wheel 1, and the hydraulic fluid is fed to a power actuator 6 via a control valve 3 whereby controlling the steering wheel 1 is varied. In this case, a power-assisted quantity variable setter 11 is connected to the input side of the controller 8, that is, the line of a car speed sensor 10 while a power-assisted quantity indicator 12 is as well connected to the output side. With the said assisted quantity variable setter 11 adjusted when necessary, such a power-assisted quantity as optimum for driver's steering capacity is thus easily secured.