A rotation driving device includes: a casing; a stator holding part; a cylindrical member; a flange extending from an end of the cylindrical member in the axial direction toward a rotating shaft, and facing an end of the stator holding part in the axial direction; and a fastening member fastened to the end of the stator holding part in the axial direction via the flange. The flange has a through-hole extending through the flange in the axial direction, and in which the fastening member is inserted. The through-hole has a diameter smaller than that of a head of the fastening member, and larger than that of a screw part of the fastening member. The rotating shaft, the rotor, the stator, the stator holding part, and the cylindrical member are arranged in this order in the radial direction in the casing, and are concentrically arranged.