A printing apparatus includes a housing including a feeding tray and an ejecting tray, an image forming unit disposed in the housing, a drive motor disposed in the housing, and a driving device disposed in the housing and driven by the drive motor. The driving device is adapted to convey a sheet of paper from the feeding tray onto the ejecting tray, and includes first and second driving units. The first driving unit includes a sun gear rotatable about an axis, a planet carrier rotatable about the axis, and a planetary gear disposed rotatably on the planet carrier and meshing with the sun gear. The second driving unit includes a driven gear meshing with the planetary gear. The planet carrier is pivotable relative to the sun gear to remove the planetary gear from the driven gear.