A sheet conveying apparatus for an image information processor includes a driving apparatus having a sheet supply opening and a sheet discharge opening arranged above and below and in the same direction, and a registration roller, a delivery roller, a scan roller, and a delivery roller arranged in order along a sheet conveying path formed in an opening curve of a substantially C-shape. The driving apparatus drives the rollers in mutual operations with selective combinations according to a sheet conveying process, and includes a driving motor controlled to change driving modes in the forward and reverse directions, and a power switching device for selectively transferring a rotational force to first and second power transmission systems according to the driving modes of the driving motor, whereby changes in sheet conveying speeds are controlled to secure reliability in the skew-feed correction of a sheet when supplying a large capacity of sheets at a high speed, and to adjust image resolution by mode.