A color electrophotographic image forming apparatus includes plural cartridge mounting portions for demountably mounting independently removable cartridges, a moving unit that includes the cartridge mounting portions and is movable between an image forming position and a mounting and demounting position for mounting and demounting the cartridges, and a mounting and demounting position locking member for locking the moving unit in the mounting and demounting position to prevent movement to the image forming position when at least one of the cartridges is not mounted in the corresponding cartridge mounting portion. The mounting and demounting position locking member is movable from an unlocking position to a locking position in interrelation with demounting of any one of the cartridges from its corresponding cartridge mounting portion, and to the unlocking position when all of the plurality of cartridges are mounted in their corresponding plurality of cartridge mounting portions.