Patent ID: 7917068

Claim:
A developing device disposed facing an image bearing body that bears a latent image, said developing device including a developer bearing body that bears a developer for developing said latent image, said developer comprising mother particles and external additives, wherein a liberation amount T (weight parts) of said external additives liberated from said mother particles with respect to 100 weight parts of said mother particles, a surface roughness Rz (m) of said developer bearing body, and a circumferential speed Vd (mm/s) of said developer bearing body satisfy the following relationships: 1.326×10 −1 ≦T≦ 2.142×10 −1 (weight parts), 7.1×10 −6 ≦Rz≦ 15.0×10 −6 (m), 161.5≦Vd≦189.2 (mm/s), and 4.98×10 −6 ≦( T×Rz/Vd )≦1.99×10 −5 (s).