A positively chargeable developer is provided which is capable of providing stable image quality without causing any image defect even in long-term use. The developer includes at least positively chargeable toner particles each containing at least a binder resin and magnetic iron oxide, silica and an inorganic fine powder. A unconfined yield strength at a major consolidation stress of 5 kPa of the developer is in the range of 0.1 to 2.5 kPa, and a unconfined yield strength at a major consolidation stress of 20 kPa of the developer is in the range of 2.5 to 5.5 kPa.