A cartridge configured to be mountable to a cartridge mounting part of a stapler main body, the stapler main body comprising: the cartridge mounting part to which the cartridge configured to accommodate therein a plurality of staples can be mounted; a feeding part configured to feed the accommodated staples toward a front end face of the cartridge and to expose at least one staple from the front end face; a forming part configured to bend the staple exposed from the front end face in a direction following the front end face, thereby forming the same into a U-shape including a pair of leg portions (Sb) and a crown portion (Sa) connecting end portions of the pair of leg portions (Sb); and a striking part configured to move the staple formed into the U-shape in a striking direction in which the staple is bent, thereby striking the staple into sheets placed at an end of the striking part, wherein the cartridge comprises: a staple support part (250, 250B) provided on the front end face so as to be located inside the pair of leg portions (Sb), the staple support part (250, 250B) including an inclined surface protruding obliquely from the front end face in the striking direction and being displaceable in a direction perpendicular to the front end face, and the staple support part (250, 250B) configured to support the crown portion (Sa) with the inclined surface and the pair of leg portions (Sb) with side edge portions (256, 256B) of the inclined surface when the staple is moved in the striking direction, characterized in that each of the side edge portions (256, 256B) has: a connection portion (256A, 256Ba) continuing to the inclined surface and extending from the inclined surface in an opposite direction to a feeding direction, in which the feeding part feeds the staple, by a first length; and a leg portion contact portion (256c, 256Bc) extending with being folded from a tip end portion of the connection portion (256A, 256Ba) in the feeding direction by at least the first length, and configured to support a corresponding one of the pair of leg portions (Sb) from an inner side thereof. configured to be mountable to a cartridge mounting part of a stapler main body, the stapler main body comprising: the cartridge mounting part to which the cartridge configured to accommodate therein a plurality of staples can be mounted; a feeding part configured to feed the accommodated staples toward a front end face of the cartridge and to expose at least one staple from the front end face; a forming part configured to bend the staple exposed from the front end face in a direction following the front end face, thereby forming the same into a U-shape including a pair of leg portions (Sb) and a crown portion (Sa) connecting end portions of the pair of leg portions (Sb); and a striking part configured to move the staple formed into the U-shape in a striking direction in which the staple is bent, thereby striking the staple into sheets placed at an end of the striking part, wherein the cartridge comprises: a staple support part (250, 250B) provided on the front end face so as to be located inside the pair of leg portions (Sb), the staple support part (250, 250B) including an inclined surface protruding obliquely from the front end face in the striking direction and being displaceable in a direction perpendicular to the front end face, and the staple support part (250, 250B) configured to support the crown portion (Sa) with the inclined surface and the pair of leg portions (Sb) with side edge portions (256, 256B) of the inclined surface when the staple is moved in the striking direction, characterized in that each of the side edge portions (256, 256B) has: a connection portion (256A, 256Ba) continuing to the inclined surface and extending from the inclined surface in an opposite direction to a feeding direction, in which the feeding part feeds the staple, by a first length; and a leg portion contact portion (256c, 256Bc) extending with being folded from a tip end portion of the connection portion (256A, 256Ba) in the feeding direction by at least the first length, a connection portion (256A, 256Ba) continuing to the inclined surface and extending from the inclined surface in an opposite direction to a feeding direction, in which the feeding part feeds the staple, by a first length; and a leg portion contact portion (256c, 256Bc) extending with being folded from a tip end portion of the connection portion (256A, 256Ba) in the feeding direction by at least the first length, and configured to support a corresponding one of the pair of leg portions (Sb) from an inner side thereof.