A power steering apparatus wherein, when action of a hydraulic actuator of a source for steering assisting power is converted into steering motion, the steering momentum obtained in response to a specified magnitude of operation of the hydraulic actuator is larger at the central side of a rotation range of a steering wheel than at the end side thereof. The steering assisting power becomes larger as the steering angle becomes larger. As a result, when the steering wheel is largely operated, a burden of labor for steering is largely reduced without expecting an increase in capacity of the hydraulic actuator.