Abstract: In a power steering device for a vehicle, a first spool valve member is slidably received in a valve housing and is supplied with a steering pressure generated in response to a manual steering torque. A second spool valve member is slidably received in the first spool valve member and is supplied with a control pressure depending upon a vehicle speed. Bypass means is formed on the first and second spool valve members to be actuated by the control pressure to communicate both cylinder chambers of a manual steering torque supplementing hydraulic actuator with each other. Relative displacement between the first and second spool valve members is caused by the steering pressure to act to close the bypass means.