A sheet post-processing apparatus includes: a sheet conveying unit that conveys a sheet; a sheet accumulating feed path that is arranged on a downstream side of the sheet conveying unit in a sheet conveying direction and being capable of accumulating therein a plurality of sheets; a stopping member that stops a leading edge of a sheet conveyed into the sheet accumulating feed path; a width aligning unit that aligns a width of the sheet stopped by the stopping member and accumulated in the sheet accumulating feed path; and a control unit that performs control to cause: the sheet conveying unit to convey a sheet into the sheet accumulating feed path; the stopping member to stop the leading edge of the sheet; and the width aligning unit to align the width of a sheet every time a sheet is accumulated in the sheet accumulating feed path.