An image forming device includes a main body, a support unit, a driving unit, a developer cartridge, a moving member, a transmitting member, and a detection member. The support unit can be pulled out from the main body in a removing direction. The developer cartridge is detachably mounted in the support unit and has a driving member. The driving member is driven by the driving unit when the developer cartridge is mounted in the support unit. The moving member moves when the driving member is driven by the driving unit. The transmitting member is provided to the support unit and is rotatable about a rotational axis which extends perpendicular to the removing direction and a longitudinal direction of a photosensitive member. When the moving member contacts the transmitting member, the transmitting member rotates. The detection member detects a rotation of the transmitting member.