A power steering, comprising: a pump driven from an engine; a flow control valve for regularizing the discharge rate of the pump varying in response to the rotational speed of the engine; a power cylinder; a distribution control valve for distributing a regularized fluid pressure from the flow control valve to opposite fluid chambers of the power cylinder; a sector gear meshed with a rack formed on the piston of the power cylinder and rotatable by operation of the power cylinder; a sector shaft having the sector gear formed integrally therewith and displaceable in the axial direction for adjusting the preload on the meshed rack and sector gear; a preload control cylinder for axially displacing the sector shaft, the preload control cylinder including a piston connected to the sector shaft and having different pressure receiving areas on the axially opposite ends thereof; a first fluid passage for conducting part of the pressurized fluid being sent from the pump to said flow control valve, to one of fluid chambers defined in the preload control cylinder by the piston; and a second fluid passage for conducting part of the pressurized fluid being fed from the flow control valve to the distribution control valve to the other fluid chamber in the preload control cylinder.