A reduction gear comprising: a shaft; an externally toothed gear that is externally fitted to the shaft; and a bearing that is disposed between the shaft and the externally toothed gear, wherein the shaft or the externally toothed gear serve as at least one of an inner ring and an outer ring of the bearing, wherein an axial movement of a rolling element (62, 63) of the bearing is restricted by a first position restriction member fixed to or integrated with the shaft and a second position restriction member fixed to or integrated with the externally toothed gear, whereby an axial movement of the externally toothed gear with respect to the shaft is restricted, wherein the bearing comprises a first rolling element and a second rolling element that are arranged in a line in the axial direction, wherein the first position restriction member comprises a position restriction portion (60A, 60B) that is located outside of the first rolling element and the second rolling element in the axial direction, wherein the second position restriction element is located between the first rolling element and the second rolling element in an axial direction, wherein the rolling element (62, 63) is slid with the second position restriction member, or slid with a thrust plate (70, 71) which is interposed between the second position restriction member and the rolling element (62, 63) wherein, viewed from a radial direction of the shaft, the position restriction portion (60A, 60B) of the first position restriction member does not overlap with the second position restriction member, and when the thrust plate (70, 71) is interposed, the position restriction portion (60A, 60B) also does not overlap with the thrust plate (70, 71), and characterized in that the bearing is provided with a retainer which retains the first rolling element and the second rolling element, the position restriction portion (60A, 60B) of the first position restriction member is located inside of the retainer in the radial direction, and the second position restriction member is located outside of the retainer in the radial direction. a shaft; an externally toothed gear that is externally fitted to the shaft; and a bearing that is disposed between the shaft and the externally toothed gear, wherein the shaft or the externally toothed gear serve as at least one of an inner ring and an outer ring of the bearing, wherein an axial movement of a rolling element (62, 63) of the bearing is restricted by a first position restriction member fixed to or integrated with the shaft and a second position restriction member fixed to or integrated with the externally toothed gear, whereby an axial movement of the externally toothed gear with respect to the shaft is restricted, wherein the bearing comprises a first rolling element and a second rolling element that are arranged in a line in the axial direction, wherein the first position restriction member comprises a position restriction portion (60A, 60B) that is located outside of the first rolling element and the second rolling element in the axial direction, wherein the second position restriction element is located between the first rolling element and the second rolling element in an axial direction, wherein the rolling element (62, 63) is slid with the second position restriction member, or slid with a thrust plate (70, 71) which is interposed between the second position restriction member and the rolling element (62, 63) wherein, viewed from a radial direction of the shaft, the position restriction portion (60A, 60B) of the first position restriction member does not overlap with the second position restriction member, and when the thrust plate (70, 71) is interposed, the position restriction portion (60A, 60B) also does not overlap with the thrust plate (70, 71), and characterized in that the bearing is provided with a retainer which retains the first rolling element and the second rolling element, the position restriction portion (60A, 60B) of the first position restriction member is located inside of the retainer in the radial direction, and the second position restriction member is located outside of the retainer in the radial direction.