A sheet post-processing apparatus includes a processing tray, a shift member, a discharge tray, a discharge roller pair, and a pressing member. The shift member moves a sheet loaded on the processing tray in a sheet width direction. The discharge roller pair discharges a sheet on the processing tray onto the discharge tray. The pressing member presses down a sheet discharged onto the discharge tray. The pressing member has an arm portion which rotates in the sheet conveyance direction about a rotation fulcrum, and a roller which is attached to the arm portion to be rotatable in the sheet width direction, and the pressing member is selectively disposed in a first position where the roller presses down the upstream-side end part of a sheet discharged onto the discharge tray, or in a second position where the roller contacts a lower surface of a sheet on the processing tray.