A developer includes a toner containing toner mother particles and external additives added to the toner mother particles. The toner mother particles contain at least a resin and a coloring agent. 1.5 to 3.0 weight parts of the external additives are added to 100 weight parts of the toner mother particles. The toner has a mean volume diameter in a range from 6.5 to 8.0 .mu.m, and a surface roughness Rzjis in a range from 75.3 to 236.9 nm as measured using a scanning probe microscope.