In a document scanning device, a flatbed scanner has a transparent platen for supporting a document, and performs flatbed scanning on the document, a cover operable and closeable relatively to the flatbed scanner is pivotally connected to the flatbed scanner, and a presser assembly is detachably disposed on a lower surface of the cover. The presser assembly has a first pressing plane and a second pressing plane opposite to each other. The cover and the presser assembly respectively have detachable docking structures disposed between the first pressing plane and the second pressing plane, so that a user can detach the presser assembly from the lower surface of the cover, or attach the presser assembly to the lower surface of the cover, and that the first pressing plane and the second pressing plane can directly press the document onto the transparent platen of the flatbed scanner in two different used states.