Image forming apparatus and cartridge

An image forming apparatus for forming an image on a recording material, comprising:

• a plurality of cartridges each including a developer accommodating portion for accommodating a developer for developing electrostatic latent image formed on a photosensitive member;
• a cartridge supporting member including a plurality of mounting portions in which said plurality of cartridges is detachably mountable, said cartridge supporting member being movable between an inside position inside a main assembly of said image forming apparatus and an outside position outside the main assembly;
• and
• a plurality of preventing members each provided movably in an associated cartridge, corresponding to the plurality of mounting portions, wherein each preventing member is movable, when said cartridge supporting member is moved from the outside position to the inside position, between a first position in which each preventing member prevents movement of said cartridge supporting member from the outside position to the inside position by contacting the main assembly and a second position, retracted from the first position, in which each preventing member permits the movement of said cartridge supporting member;
• an opening, provided in said cartridge supporting member, for permitting passing of an associated preventing member located at the first position through said outside only when an associated cartridge is mounted in an associated mounting portion,
• wherein the associated preventing member is retracted into the second position in contact with said cartridge supporting member when the associated cartridge is mounted in the associated mounting portion.