A sheet post-processing apparatus includes: a sheet stack tray; a rear-end-position regulating member, against which a rear end of the sheet on the tray is butted to align a position of the sheet in a sheet conveying direction to the stack tray, the rear end of the sheet being a rear end in the conveying direction; and a roller member that comes in contact with an upper surface of the sheet conveyed to an upper side of the tray, before the sheet is stacked on a stacking surface on the tray, and conveys the sheet stacked on the stacking surface toward the rear-end-position regulating member, wherein a rotation speed before stacking is set to be smaller than a rotation speed after stacking, and the rotation speed of before stacking is greater than zero.