A scanning device includes a hollow housing, a holding plate mounted to an upper portion of the housing, a guiding rod mounted in the housing and spaced from the holding plate with a predetermined distance, a reading unit slidably mounted to the guiding rod, and a flexible cable received in the housing. The flexible cable has a restrictive plate and a conducting cable attached to a top of the restrictive plate. The restrictive plate has at least one long side raised upwardly. The flexible cable is received in the housing in a folding manner, with a lower end thereof where the raised side faces upwards connected to the system controller, and an upper end thereof where the raised side faces downwards connected to the reading unit, forming an inverted-U folding portion. The raised side at the folding portion is unfolded for keeping the folding portion in shape, in scanning process.