A duplex scanning apparatus includes a scan case including a platen glass, a first scanning module disposed inside the scan case, a scanning module moving unit that is disposed inside the scan case perpendicular to the first scanning module and guides a movement of the first scanning module, and an automatic document feeding apparatus disposed on a top side of the scan case to cover the platen glass including a feeding frame in which a document moving route is formed, a scanning module opening formed on an upper side of the document moving route in the feeding frame, a second scanning module disposed in the scanning module opening, and a scanning module adjusting unit formed to rotate the second scanning module by a predetermined angle based on a point of the feeding frame with respect to the scanning module opening.