A post-processing device includes a transport section transporting a sheet; a load section loading the sheet thereon; a first aligner moving the sheet while being in contact with a surface thereof to align the sheet; a second aligner moving the sheet while being in contact with an edge thereof to align the sheet; an alignment controller controlling the aligners to align the sheet based on a first mode in which they simultaneously align the sheet, and based on a second mode, for every predetermined number of sheets, in which one aligner aligns the sheet after the other aligner completes the alignment process; and a transport controller causing the transport section to transport the sheet at a reduced speed for every predetermined number of sheets so that the sheet reaches the load section after completion of the second-mode alignment process performed after a previous sheet is loaded on the load section.