A sheet transporting device applicable to a sorter of the type having a plurality of bins arranged one above another for receiving sheets sequentially driven out of an image forming apparatus includes a top tray disposed above an uppermost one of the bins. A sheet stack is pulled out from each bin, transported upward, and then discharged onto the top tray. This not only promotes easy take-out of sheet stacks from the sorter but also allows the number of sheet stacks greater than the number of bins to be produced without interruption.