An image forming apparatus includes: a casing; a toner cartridge; a drum cartridge; a main electrode; a first reading portion; and a controller. The toner cartridge is attachable to the drum cartridge and includes: a developing roller; and a developing electrode electrically connected to the developing roller. The drum cartridge is attachable to the casing and includes: a photosensitive drum; a pressing member; and a drum memory. The pressing member presses the toner cartridge toward the photosensitive drum so that an outer circumferential surface of the developing roller contacts an outer circumferential surface of the photosensitive drum. The drum memory stores a pressing force value indicating a pressing force to be applied by the pressing member. The controller is configured to perform: reading, through the first reading portion, the pressing force value from the drum memory; and applying a voltage to the main electrode based on the pressing force value.