A remanufacturing method for a developer supply container detachably mountable to a main assembly of an image forming apparatus, the developer supply container including a frame, a developer accommodating portion for accommodating a developer to be used by a developing device of the image forming apparatus, a developer filling opening for filling the developer into the developer accommodating portion, a capping member for closing the developer filling opening, and a cap covering member covering the capping member, the cap covering member being fixed by welding to the frame, the remanufacturing method including a cap covering member dismounting step of dismounting the cap covering member from the frame by separating cap covering member from the frame at a welded portion; a capping member dismounting step of dismounting the capping member to open the developer filling opening; a developer filling step of filling the developer with the developer filling opening; a capping member mounting step of closing the developer filling opening by a capping member; a cap covering member mounting step of mounting the cap covering member to the frame.