An image forming unit has a configuration in which, when an opening-closing member causes respective first openings to be opened by the engagement of the opening-closing member and an engaging section in association with an operation of attaching a developer container to an attachment unit, a first surface and a second surface are separated away from each other until arrival of the first openings at positions corresponding to respective second openings, and the first surface and the second surface are brought into proximity to each other upon the arrival of the first openings at the positions corresponding to the respective second openings.