Abstract: A sorter for sorting sheets discharged from an image forming apparatus, comprising a sorter frame; a plurality of bins disposed in the vertical direction, for making stacks of the discharged sheets; a bin frame incorporating the bins and having an opening on a front side adapting the sorter for a stack-removal operation; a processing mechanism provided on the image-forming-apparatus side of the bins, for processing the stacks; a first driving mechanism for driving a bin at a bin-processing position opposite the processing mechanism to slide toward the processing mechanism for feeding the image-forming-apparatus side end of said stack to the processing mechanism; a single unit slide guide for guiding a bin at the bin processing position toward the processing mechanism; a second driving mechanism including a pair of rods disposed vertically on the front and back sides of the sorter frame, the rods move the bins and the bin frame vertically and support the bins from either side at a position inward from an image