Abstract: A power steering unit capable of finely controlling the steering assistance power generated by a hydraulic actuator in accordance with the steering direction and driving condition without requiring a complex structure is provided at low cost. The right steering assistance power generating state or the left steering assistance power generating state can be alternatively selected by switching the flow path of hydraulic fluid to the hydraulic actuator 10 for generating the steering assistance power with a motor-operated switching valve 23. The switching valve 23 is controlled so that the steering assistance power acts in accordance with the determined steering direction, and an electric motor 22 for driving a pump 21 is controlled so that the pressure of the hydraulic fluid discharged from the pump 21 is varied in accordance with the determined driving condition.