A sheet post-processing apparatus is known which executes a post-processing such as a stapling processing on sheets loaded on a processing tray. In order to adjust deviation between the sheets loaded on the processing tray which are subjected to the post-processing, the sheet post-processing apparatus includes a horizontal aligning member and a vertically aligning member. The horizontal aligning member is a member for aligning a deviation in the width direction of the sheet. The vertical aligning member is a member for aligning a deviation in a direction orthogonal to the width direction of the sheet.
The above vertical aligning member is fixed against the sheet post-processing apparatus. Thus, the aligning processing by vertical aligning member might cause the deviation of sheets to arise, depending on the position of sheet aligning.