A remanufacturing method for remanufacturing a second developing device from a first developing device, the first developing device including a frame provided with a developer accommodating chamber for accommodating a developer, the frame having an opening for communicating the developer accommodating chamber with the outside of the frame; and a first cap member configured to seal the opening, the first cap member being adhesively bonded to a first region of the frame with a first adhesive capable of dissolving the frame, and the remanufacturing method including: removing the first cap member from the first region such that a rough surface is formed in the first region; filling the developer accommodating chamber with the developer; and bonding a second cap member different from the first cap member to a second region of the frame different from the first region to seal the opening with the second cap member.