A compact scanner apparatus is provided that is suitable for constituting an information display system by being stored in a pedestal which supports a display apparatus. The scanner apparatus is composed of an upper unit provided with an automatic document feeder and a lower unit provided with an image reading device, wherein a width guide rack mechanism having a function of detecting an original size is independent from a paper feed tray and disposed above the paper feed tray. Thereby, it is possible to store the paper feed tray and the whole of the width guide rack mechanism within the apparatus.