An image forming apparatus has: a photosensitive cartridge; a development cartridge detachably mounted to the photosensitive cartridge; a main body in which the photosensitive cartridge is detachably mounted; a first sensor; a second sensor; and a control unit. Where the second sensor is brought into a second state after being temporarily brought into a first state, it is determined that the development cartridge is a new one. Where the second sensor is in the first state and the first sensor receives light within a predetermined period of time, it is determined that both the development cartridge and the photosensitive cartridge are not mounted Where the second sensor is in the first state, and the first sensor does not continuously receive the light for a predetermined period of time, it is determined that the photosensitive cartridge is mounted and the development cartridge is not mounted.