An image forming apparatus is provided which can be switched between states in which a developing roller is attached to an image carrier body by applying a pressing force to a developing cartridge and a state in which the developing roller can be released from attachment from the image carrier body. When an operation part of a toner cartridge is arranged at an installation position a pressing force can be applied to a developing cartridge by protruding parts fitting with spring parts, and a developing roller can be attached to a photoconductor drum by the applied pressure. When the operation part is arranged at a removal position, the fitting can be undone, causing the applied pressure to be released.