An image forming device includes a movable holding member, a plurality of operation members and a plurality of developer cartridges detachably mountable on the holding member. The holding member has a plurality of photosensitive members and developing devices. Each operation members is disposed on the holding member in correspondence with each developing device. Each of the photosensitive member, the operation member and the developer cartridge extends in a first direction. Each developer cartridge is formed with an opening and has a shutter member linearly movable between an open position and a closed position in the first direction. The shutter member opens the opening at the open position to allow developer to flow and closes the opening at the closed position to prevent developer from flowing. Each operation member is linearly movable in the first direction to move the shutter member between the open position and the closed position.