A steering system is provided in which a bearing of a tension pulley has a reduced load-carrying capacity. A belt tension adjusting mechanism has a seat provided on an inner surface of a reduction gear housing so as to be able to swing, a rod that is in abutting contact with the seat (bent portion), a feed nut that is screw-threaded over the rod, and a spring member (helical torsion spring) that is fixed to the feed nut at its one end and to the reduction gear housing at the other end. When the belt is loosened, the feed nut is rotated by an elastic force of the spring member, and in conjunction with the rotation, the rod moves away from the feed nut to push the seat (bent portion).