POWER STEERING

PROBLEM TO BE SOLVED: To stably and silently perform transmission from a steering assist motor to a steering shaft by adjusting the engagement of a plurality of feed rings with a thread groove formed on the outer periphery of the steering shaft. SOLUTION: An inner cylinder 11 holding two feed rings R1, R2, and an inner cylinder 12 holding two other feed rings R3, R4, are coaxially held inside an outer cylinder 10 rotatably supported to a transmission housing H, to constitute a rotating cylinder 1. The respective feed rings R1-R4 are engaged with a thread groove 20 on the outer periphery of a rack shaft 2 inserted through the inside of the rotating cylinder 1, and the engaged state can be appropriately adjusted by moving the inner cylinders 11, 12 in the axial length direction inside the outer cylinder 10.