A developer supply device for supplying an image forming apparatus with a developer includes a developer accomodating container having an opening for supplying the developer, and a member for opening and closing the opening of the container. The developer accomodating container is slid to be positioned at a predetermined position. The direction of movement of the openable and closable member to open the opening coincides with the direction of the sliding movement for being positioned. A force needed for the movement of the openable and closable member is arranged to be larger than a force needed for the sliding movement of the developer accomodating container. The device also includes a regulating member, which prevents the developer accomodating container from being moved from the predetermined position when the openable and closable member is opened. In order to prevent mismounting of an improper developer accomodating container, engagement between the developer accomodating container and a mounting portion for the container is arranged to be different in accordance with the kind of the developer.