A scanning device is capable of scanning both sides of a medium and includes a lens module, an optical-electric coupling unit, and a processor. The lens module faces the medium to be scanned. The optical-electric coupling unit is optically connected to the lens module. The processor is optically connected to the optical-electric coupling unit, and includes a light emitting unit and a light receiving unit. The light beams emitted from the light emitting unit are directed into the lens module through the optical-electric coupling unit, and illuminate the medium to be scanned. The light beams reflected by the medium enter into the optical-electric coupling unit through the optical-electric coupling unit, and then to the light receiving unit. The processor processes the reflected light beams into electrical signals to obtain scanning signals.