An image scanning device includes a bottom wall, a surrounding wall extending upwardly from the bottom wall, a frame connected to the surrounding wall and having a first side plate, and a transparent panel fixed to the frame and having a lateral side supported by an upper part of the first side plate. A contact image sensor module is disposed on the bottom wall transverse to the first side plate, and includes a housing having a first short side wall spaced apart from the first side plate by a first distance less than or equal to 2 mm, and a plurality of sensors, one of which that is closest to the first short side wall is spaced apart from an outer surface of the first short side wall by a second distance less than or equal to 2.5 mm.