In a post-processing apparatus in which sheets are stacked in a stacker section and arranged to be subject to post-processing, the stacker section is provided with a sheet ejection section which subsequently ejects the sheets one by one or two or more sheets overlapped with each other, wherein the sheet ejection section is provided with a corrugation application member to apply corrugation onto the sheet to be ejected and to change extent of the corrugation to be applied.