A power steering apparatus is furnished with a rotary cylinder supported by restraining the movement in the axial direction and rotating coaxially with a steering shaft by the transmission of movement from the motor, a feed ring fixed in the rotary cylinder with eccentricity by a predetermined angle and a predetermined distance to the axial center of the steering shaft or a plurality of feed rings which are fixedly disposed in inclination at equal angle and eccentricity in equal distance to the axial center of the steering shaft, being fixed to the inside of the rotary cylinder with equal disposition of the respective eccentric positions in the circumferential direction, thus it generates low noise and can convert rotation of the motor to movement of the steering shaft in the axial direction to take the place of a ball screw mechanism, and can be constituted by a simple structure.