Fuente: WIPO "circular economy" A power transmission device includes: a fixing member having a cylindrical surface; an output shaft having a facing surface facing the cylindrical surface; an input shaft having a pressing portion disposed between the cylindrical surface and the facing surface; and a pair of rolling elements. The facing surface includes a recessed surface. The recessed surface has a bottom surface and a pair of pressed surfaces. The bottom surface has a central surface and a pair of cam surfaces. A distance between the cam surface and the cylindrical surface increases from the central surface toward the pressed surface. A distance between the cam surface and the cylindrical surface is smaller than a diameter of the rolling element in the portion closer to the central surface, and is greater than the diameter of the rolling element in the portion closer to the pressed surface.