A steering apparatus comprising: a steering shaft; a steered shaft supported by a housing so as to be slidable in an axis direction of the steered shaft and configured to reciprocate in the axis direction via a rack-and-pinion mechanism in accordance with a steering angle of the steering shaft so as to steer steered wheels; a ball screw mechanism including a rolling element screw portion having a first screw groove (21b1) formed on an outer peripheral surface of the steered shaft, a rolling element nut having a second screw groove (33a1) formed on an inner peripheral surface of the rolling element nut so as to correspond to the first screw groove (21b1), a connecting member including a connecting passage connected to both ends of a spiral raceway formed between the first screw groove (21b1) and the second screw groove (33a1) so as to form a circulation passage together with the spiral raceway, and a plurality of rolling elements arranged and accommodated in the circulation passage, the circulation passage being continuous; and a motor fixed to the housing so as to rotate the rolling element nut around an axis of the steered shaft, and including an output shaft offset from the steered shaft; wherein the steering apparatus further includes a belt transmission mechanism including a toothed drive pulley provided on the output shaft so as to be rotatable integrally with the output shaft, a toothed driven pulley integrally provided on the rolling element nut, and a toothed belt that transmits a driving force between the drive pulley and the driven pulley; and a radial clearance in the spiral raceway varies in a circumferential direction depending on a direction of a tensile force of the toothed belt, characterized in that the plurality of rolling elements includes large-diameter rolling elements and small-diameter rolling elements having a diameter smaller than that of the large-diameter rolling elements by a prescribed diameter difference, each of the small-diameter rolling elements being disposed between the large-diameter rolling elements, and the prescribed diameter difference is set such that when a magnitude of power transmitted between the first screw groove and the second screw groove (33a1) is a prescribed value or less, only the large-diameter rolling elements transmit the power between the first screw groove and the second screw groove (33a1) in the spiral raceway, and when the magnitude of the power transmitted between the first screw groove (21b1) and the second screw groove (33a1) exceeds the prescribed value, both the large-diameter rolling elements and the small-diameter rolling elements transmit the power between the first screw groove and the second screw groove (33a1) in the spiral raceway. a steering shaft; a steered shaft supported by a housing so as to be slidable in an axis direction of the steered shaft and configured to reciprocate in the axis direction via a rack-and-pinion mechanism in accordance with a steering angle of the steering shaft so as to steer steered wheels; a ball screw mechanism including a rolling element screw portion having a first screw groove (21b1) formed on an outer peripheral surface of the steered shaft, a rolling element nut having a second screw groove (33a1) formed on an inner peripheral surface of the rolling element nut so as to correspond to the first screw groove (21b1), a connecting member including a connecting passage connected to both ends of a spiral raceway formed between the first screw groove (21b1) and the second screw groove (33a1) so as to form a circulation passage together with the spiral raceway, and a plurality of rolling elements arranged and accommodated in the circulation passage, the circulation passage being continuous; and a motor fixed to the housing so as to rotate the rolling element nut around an axis of the steered shaft, and including an output shaft offset from the steered shaft; wherein the steering apparatus further includes a belt transmission mechanism including a toothed drive pulley provided on the output shaft so as to be rotatable integrally with the output shaft, a toothed driven pulley integrally provided on the rolling element nut, and a toothed belt that transmits a driving force between the drive pulley and the driven pulley; and a radial clearance in the spiral raceway varies in a circumferential direction depending on a direction of a tensile force of the toothed belt, characterized in that the plurality of rolling elements includes large-diameter rolling elements and small-diameter rolling elements having a diameter smaller than that of the large-diameter rolling elements by a prescribed diameter difference, each of the small-diameter rolling elements being disposed between the large-diameter rolling elements, and the prescribed diameter difference is set such that when a magnitude of power transmitted between the first screw groove and the second screw groove (33a1) is a prescribed value or less, only the large-diameter rolling elements transmit the power between the first screw groove and the second screw groove (33a1) in the spiral raceway, and when the magnitude of the power transmitted between the first screw groove (21b1) and the second screw groove (33a1) exceeds the prescribed value, both the large-diameter rolling elements and the small-diameter rolling elements transmit the power between the first screw groove and the second screw groove (33a1) in the spiral raceway.