Patent ID: 7440718

Claim:
A developing apparatus comprising: a rotatable developer carrying member carrying a developer thereon to develop an electrostatic image formed on an image bearing member with the developer; non-rotatable magnetic field generating means provided inside said developer carrying member for magnetically attracting the developer toward said developer carrying member; and a developer amount regulating member contacting with said developer carrying member to regulate an amount of the developer carried on said developer carrying member, wherein said developer carrying member is provided with an elastic layer on a surface thereof, and is urged against said image bearing member, wherein the developer is a mono-component magnetic toner having a mean degree of circularity of 0.965 or greater, and wherein a voltage is applied between said developer carrying member and said developer amount regulating member through the developer, and wherein the following expressions and are satisfied: | Br|/|B|≧ 0.5 Nsb /( Bs×R )≦0.5, and where B (G) is a magnetic flux density formed on the surface of said developer carrying member by said magnetic field generating means at a contact position between said developer amount regulating member and said developer carrying member, Nsb (mm) is a contact width between said developer amount regulating member and said developer carrying member, Br (G) is a perpendicular component of the magnetic flux density (G) in a direction perpendicular to the surface of said developer carrying member, Bs (rad) is a half-value width of the perpendicular component of the magnetic flux density formed on the surface of said developer carrying member by a nearest magnetic pole of magnetic poles of said magnetic field generating means at the contact position, and R (mm) is a radius of said developer carrying member.