A cartridge includes: a first frame member which has an opening through which a developer accommodated therein is fed; a sealing member which seals the opening and which is pulled out to unseal the opening; a second frame member which sandwiches the sealing member with the first frame member; a welding portion which is formed on one of the first frame member and the second frame member and adapted to weld the first frame member and the second frame member at an area outside the opening; and a sandwiching portion which is formed on one of the first frame member and the second frame member and which is melted with the welding of the welding portion at an area outside the opening and inside the welding portion to sandwich the sealing member between the first frame member and the second frame member.