To prevent a sheet from being clogged between a processing tray and a stapler.

A finisher includes: a processing tray 129 for mounting a sheet thereon; staplers 132 for binding sheets mounted on the processing tray with a head part for projecting a needle and an anvil part for folding the needle at a position with the intervention of gaps G1 and G2 from an edge part of the processing tray; a conveyance roller for conveying the sheets mounted on the processing tray to the staplers to make the end parts of the sheets advance between the head part and the anvil part; and guide plates 175 and 185 for guiding the end parts of the sheets from the processing tray to the staplers while advancing from the processing tray over the head part or the anvil part provided side by side with the processing tray 129 between the head part and the anvil part. The guide parts prevent the sheets from passing through on the gaps to enter into the gaps.