A sheet post-processing apparatus of the invention includes a sheet guiding unit configured to have plural components including paper carrying components be attached thereto, a tray onto which a sheet of paper is discharged, and a protection cover attached to the sheet guiding unit at a portion in close proximity to the tray side. A protection cover has a cover main body, a screw attachment portion, a screw cover that covers the screw attached to the screw attachment portion, and a slit used for the tip end of the screw cover to be inserted into the cover main body to be fixed thereto.