The developing device 100 includes a stirrer and transferor 122, 124, a magnetic roller 130, and a developing roller 140, that are disposed in a housing 110 which contains the two-component developing agent including the magnetic carrier and the non-magnetic toner, wherein volumetric mean particle size of the non-magnetic toner is set in a range from 6 to 11 .mu.m and proportion of toner particles not larger than 4 .mu.m is set to 8% by number or less, thereby making it possible to prevent imaging defect (ghost) and sticking of the toner onto the developing roller from occurring.