<p>A power steering system with which no deterioration in steering feeling occurs when a control flow of working fluid changes. A valve mechanism V is made up of a power cylinder control valve CV for controlling a control flow Q and distributively supplying it to a power cylinder C and a bypass control valve BV connected in parallel with the cylinder control valve CV. The bypass control valve BV is normally closed, but while the control flow Q is increasing over a range of from a minimum flow Q1 to a maximum flow Q2 available for generating assist force the bypass control valve opens and returns a part of the control flow Q to a tank so that the pressure difference between the pressure chambers of the power cylinder C rises gently and the driver does not experience a disconcerting feeling such as one of the steering wheel suddenly being taken over. <IMAGE></p>
