According to an embodiment, a developing device, comprising: a developing unit configured to store an initial two-component developer including an initial toner containing silica externally added and a carrier and to form a toner image on an image bearing member with the two-component developer; a discharging section configured to discharge a part of the initial developer from the developing unit; and a developer supplying unit configured to supply a supply developer including a supply toner containing silica externally added and the carrier to the developing unit, the amount of silica added to the supply toner being smaller than the amount of silica added to the initial toner.