1. A document imager comprising: a document bed plate on which an original document is mounted and which has a specific pattern formed on a surface thereof; an imaging section that images the original document mounted on the document bed plate; a first stillness judging section which judges stillness of the original document mounted on the document bed plate from at least one of (i) a discontinuity of the pattern of an outer peripheral portion in an image of the document bed plate obtained by the imaging section and (ii) a change in the outer peripheral portion in the image of the document bed plate; a second stillness judging section which judges the stillness of the original document mounted on the document bed plate by regarding movement of apex coordinates of the original document as a change in the image of the document bed plate; and an output section which outputs the image of the original document when both the first and second stillness judging sections judge that the original document is still.