A toner cartridge is to be attached to a developing device. The developing device is provided with a developing roller comprising a rotational axis extending along a horizontal direction, a first casing, and a first transporting member. The first casing includes a developing chamber for accommodating the toner to be supported by the developing roller, a first feed opening for feeding the toner from the toner cartridge to the developing chamber, and a first return opening for returning the toner from the developing chamber to the toner cartridge. The first transporting member is located within the developing chamber. The first transporting member transports the toner within the developing chamber from the first feed opening to the first return opening. The first feed opening and the first return opening are offset along the horizontal direction. The first feed opening is located higher the first return opening.