An image forming apparatus detachably mounts a cartridge and forms an image on a recording material. The apparatus includes a cartridge positioning portion, a movable member movable between a first position for positioning the cartridge to the positioning portion when the cartridge is mounted to a main assembly of the apparatus, and a retracted position, for permitting cartridge main-assembly mounting in a cartridge longitudinal direction. The movable member has an urging member urging the cartridge to the positioning portion when the movable member takes the first position. Also provided is a guiding member movable relative to the movable member to take a guide position guiding the cartridge when the movable member takes the retracted position and a position retracted from the guide position away from the cartridge when the movable member takes the first position.