A stapler includes a striking part which causes a pair of staple legs to penetrate a sheet bundle, a bending part which bends the staple legs at a first position such that tips of the staple legs are directed inwardly, and a clincher part which bends the staple legs at a second position located closer to the sheet bundle than the first position to be entirely directed inwardly. The bending part includes a first part disposed on an inner side of the staple legs and having a first tip portion facing the staple legs at the first position, a second part disposed on an outer side of the staple legs and having a second tip portion facing the staple legs on a non-sheet bundle side than the first position, and a moving part which moves at least one of the first and second parts toward the staple legs.