A foreign substance prevention unit use with an electro-photographic
printer is installed over a waste toner injection hole such that it
closes the waste toner injection hole when a photosensitive medium is
separated from a main body of the electro-photographic printer, and opens
the waste toner injection hole when the photosensitive medium is
installed in the main body of the electro-photographic printer. The
foreign substance prevention unit is formed of an elastic material.