A developing apparatus includes an image receptor and a developing unit having a developing roller facing the image receptor. New toner can be added to the developing unit when existing toner in the developing unit is consumed. The added toner and existing toners are formed of cores and external additives. At least one of the cores or the external additives of the added toner is different from that of the existing toner. When the charge amount of the two toners are Q 1 and Q 2 , respectively, the ratio Q 1 /Q 2 is greater than 0.6 and smaller than 1.7, and the absolute values of Q 1 and Q 2 are 10 muC/g or greater, respectively.