A cover covering an image bearing member such that the image bearing member is kept unexposed includes a holding portion holding an end portion of a sealing sheet sealing an opening portion such that an initial developer is accommodated in an accommodating chamber. Due to release of the seal of the opening portion with the sealing sheet, the initial developer accommodated in the accommodating chamber moves from the accommodating chamber to a second chamber through the opening portion, and



the seal of the opening portion with the sealing sheet is released due to movement of a casing with respect to the cover and detachment of the cover from the casing, responsive to an operation of movement of a cartridge in an attachment direction, with the holding portion holding the end portion of the sealing sheet and a regulation portion regulating movement of the cover.