An image forming apparatus includes a main assembly provided with an opening and a tray for placing thereon a cartridge for forming an image, wherein the tray is movable through the opening between an image forming position where the cartridge is used for image formation inside the main assembly and a mounting and demounting position where the cartridge is exposed to an outside of the main assembly and is mountable and demountable. In addition a door opens and closes the opening, and an accommodating member accommodates a sheet on which an image is formed. When the tray is in the mounting and demounting position, the door supports the tray and the accommodating member supports the door.