A method of reattaching a toner seal to a toner frame having a developer containing portion for containing a developer therein, a developer supplying opening for supplying the developer therethrough from the developer containing portion, in order to seal the developer supplying opening, which method includes (a) the detaching step of detaching the already taken-up toner seal from a take-up spool for taking up the toner seal, (b) the sticking step of sticking the toner seal on the toner frame so as to seal the developer supplying opening, (c) the folding-back step of folding back the toner seal from the end portion of the stuck portion of the toner seal, and (d) the attaching step of attaching the free end portion of the folded-back toner seal to the take-up spool for taking up the toner seal to unseal the developer supplying opening so that the operation of a detecting lever for detecting that a predetermined amount of the toner seal has been taken up to unseal the developer supplying opening may be restricted by the toner seal.