A cartridge detachably mountable to a main assembly of an image forming apparatus includes: a frame; an accommodating portion, constituted by the frame, for accommodating a developer; a seal portion for preventing the developer from being leaking out from the accommodating portion, wherein the seal portion is formed by injection molding at a seal forming portion provided on the frame and is projected from the seal forming portion; and a sprue which is formed integrally with the seal portion by a resin material remaining in a path for permitting flow of the resin material melted when the seal portion is formed by the injection molding and which is projected from the frame in a position different from a position of the seal portion so as to be higher than the seal portion on the basis of the frame.