A turning device is provided with: a casing; a drive motor provided above the casing; a drive wheel rotated by the drive motor, the drive wheel being supported on one side of a reference plane located on the drive axis of the drive motor and parallel to the vertical direction, the drive wheel being rotatable about a reference line intersecting the reference plane; a driven wheel disposed within the casing, the driven wheel being supported so as to be rotatable about an axis parallel to the reference line, the driven wheel being connected to the drive wheel through an annular member; a first gear wheel coaxially connected to the driven wheel and having a first spur gear; a second gear wheel having a second spur gear meshing with a wheel gear which is provided coaxially with a rotating shaft extending parallel to the reference line, the second spur gear also meshing with the first spur gear of the first gear wheel; an arm member for rotatably supporting the second gear wheel; a movement mechanism for moving the arm member to thereby move the second gear wheel between a meshed position at which the second gear wheel is meshed with the wheel gear and a retracted position at which the second gear wheel is not meshed with the wheel gear; and a cover adapted to mountable and removable from the casing and covering the drive wheel.