An image forming apparatus including a latent image carrier and a developing means for charging a toner into a negative polarity by triboelectric charging, wherein the work function of the toner is set to be larger than the work function of the surface of the latent image carrier. When the apparatus includes an intermediate transfer medium, the work function of the toner is set to be larger than the work function of the surface of the intermediate transfer medium. In another embodiment, the work function _OPC of the surface of the latent image carrier, the work function _t of the toner, and the work function _TM of the surface of the intermediate transfer medium are set to satisfy a relationship _tOPCTM. These relationships help to reduce fog, and improve transfer efficiency which reduces the consumption of the toner.