An image forming apparatus is provided for forming an image on a recording material. An opening is provided to a main assembly of the image forming apparatus, with first and second openable members being movable between closed positions in which portions of the opening are closed and open positions in which portions of the opening are opened. A movable member is movable between a set position inside the main assembly and an outward position in which the movable member, having passed through the opening, is located at an outermost position. The movable member is capable of supporting a plurality of cartridges, side by side, with each of the cartridges including at least one of an image bearing member on which a latent image is to be formed and a developing roller for developing with a developer the latent image formed on the image bearing member.