Patent ID: 7853186

Claim:
A developing apparatus for developing an electrostatic image formed on an image bearing member, comprising: a developer container, which contains a magnetic developer; a first developer carrying member rotatably provided to the developer container, for carrying the magnetic developer to feed the magnetic developer to a first developing portion; a second developer carrying member rotatably provided to the developer container in the same direction as the first developer carrying member, for carrying the magnetic developer delivered from the first developer carrying member to feed the magnetic developer to a second developing portion; first magnetic field generating means arranged to be fixed in the first developer carrying member, wherein the first magnetic field generating means includes a first magnetic pole arranged to be closest to the second developer carrying member, and a second magnetic pole arranged to be adjacent to an upstream side of a movement direction of the first developer carrying member with respect to the first magnetic pole, and having a polarity opposite to the first magnetic pole; and second magnetic field generating means arranged to be fixed in the second developer carrying member, wherein the second magnetic field generating means includes a third magnetic pole which is closest to the first developing carrying member, and has a polarity opposite to the first magnetic pole, wherein a peak position, where a strength of a magnetic field of the first magnetic pole becomes a peak with respect to a circumferential surface of the first developer carrying member, is provided upstream, in the movement direction of the first developer carrying member, of a closest position between the first developer carrying member and the second developer carrying member, and wherein, the developing apparatus is configured such that a magnetic force, which is designated as Fr, is obtained by combining a magnetic force of the first magnetic field generating means and a magnetic force of the second magnetic field generating means in the vicinity of the first developer carrying member, and a direction toward a center of the first developer carrying member is designated as positive, (a) a component of the force Fr obtained in the direction of the center of the first developer carrying member is positive at least from the second magnetic pole, in the movement direction of the first developer carrying member, to the peak position, and (b) the component of the force Fr obtained in the direction of the center of the first developer carrying member changes to be negative in the area from the peak position, in the movement direction of the first developer carrying member, to the closest position between the first developer carrying member and the second developer carrying member.