A scanning device includes a base, a transparent platen above the base, a left sloped plate connecting a left platen edge of the transparent platen to a left base edge of the base, a right sloped plate connecting a right platen edge of the transparent platen to a right base edge of the base, and a scanning module below the transparent platen. The left sloped plate and the right sloped plate are disposed at two opposite sides of the transparent platen. A left angle between the left sloped plate and the transparent platen and a right angle between the right sloped plate and the transparent platen are greater than 90 degrees. The scanning module is movable along a direction parallel to the right platen edge and the left platen edge so as to acquire an image of a document placed on the transparent platen.