A stapler and a cartridge, the stapler comprising a guide member (21) having a guide piece (22) for supporting the base sides of staple legs from the inside while the staple legs are disposed in a drive-out passage (17) and passed through bound paper sheets, wherein a staple (1) forming the pair of staple legs is fed into the drive-out passage (17), the staple fed into the drive-out passage (17) is driven out to the bound sheets (P), and the staple legs passed through the bound sheets (P) are bent along the rear surface of the bound sheets.