A scanning device includes a scanning platform, a feed roller mounted above the scanning platform and rotatable to bring a sheet-like medium across the scanning platform, first and second elastic elements located under two ends of the scanning platform to press the scanning platform against the feed roller. One end of the scanning device near to the first elastic element is defined as a datum end for guiding the mediums to enter the scanning device. The first elastic element acts a greater force on the scanning platform than the second elastic element, or the distance from the first elastic element to the datum end is smaller than that from the second elastic element to the other end of the scanning device and the force from the first elastic element is equal to that from the second elastic element, so as to make the medium levelly transmitted during being scanned.