Abstract: A rotation transmitter includes a worm shaft having an hourglass-shaped portion at the center thereof, a plurality of metal balls arranged in a row on a ball circulation path, a cylindrical housing for rotatably accommodating the worm shaft therein, a worm wheel inserted in an axial slot in the housing and provided in the outer periphery thereof with ball fitting grooves for receiving the balls, and holding means for holding the worm shaft within the housing so that the worm shaft is rotatable in a state of meshing with the worm wheel via the balls. A helical ball guide groove is formed in the outer periphery of the hourglass-shaped portion of the worm shaft, and a circulation bore penetrates the hourglass-shaped portion obliquely from one side to the other side thereof so that the opposite ends thereof communicate with the associated ends of the helical ball guide groove via tangentially curved guide holes. The ball circulation path is thus constituted by the guide groove and circulation bore.