The invention provides a developing apparatus, an image forming apparatus and a toner replenishing method that can restrain deterioration of toner and can stably form high quality image. Replenishing bias voltage is applied to a developing roller and a replenishing roller to charge conductive toner kept on a surface of the replenishing roller to a predetermined amount of charge. By electric field generated between the developing roller and the replenishing roller on the basis of the applied replenishing bias voltage, charged conductive toner is made fly and replenished from the replenishing roller to the developing roller. An appropriate amount of conductive toner is kept in a toner transporting body formed on a surface of the developing roller and is supplied to a photoconductor roller.