An image forming apparatus includes a main assembly and a cartridge including at least an image bearing member. The apparatus further includes a tray drawable from the main assembly, wherein the cartridge is mountable to and dismountable from the tray in one direction and an opposite direction, respectively; and a light emission unit provided in the tray and including a plurality of light emission elements arranged in an axial direction of the image bearing member to form a latent image on the image bearing member. The cartridge is capable of being inserted into the tray by moving it in the one direction, in response to which the light emission unit is moved in a direction crossing with the one direction to outside of a movement range of insertion of the cartridge.