Patent ID: 8515320

Claim:
A developing device for developing an electrostatic latent image formed on an outer circumferential surface of an image carrier, the developing device comprising: a housing that contains therein a two-component developer and has an opening facing the image carrier; a developing sleeve that is rotatably held in the housing and partially exposed from the opening of the housing to face the image carrier, with (i) a gap between an outer circumferential surface of the developing sleeve and an upstream edge of the opening and (ii) a gap between the outer circumferential surface thereof and a downstream edge of the opening, the upstream and the downstream edges of the opening respectively being an edge located upstream and an edge located downstream in a transfer direction of the two-component developer on the developing sleeve that rotates when developing the electrostatic latent image; a magnet roller that is arranged inside the developing sleeve and has a plurality of magnetic poles arranged along a circumferential direction of the magnet roller, the plurality of magnetic poles including first and second magnetic poles, the first magnetic pole having a strongest magnetic force among the plurality of magnetic poles, the second magnetic pole having a magnetic force equal to or larger than a predetermined value and less than the magnetic force of the first magnetic pole; and a positioning member operationally connected to the magnet roller so that: (i) the magnet roller automatically rotates by virtue of rotation of the developing sleeve and rotates together with the developing sleeve when the magnet roller is in a first rotational position, and (ii) rotation of the magnet roller is inhibited when the magnet roller is in a second rotational position, the first rotational position being a position where one of the first and the second magnetic poles faces the downstream edge of the opening, the second rotational position being a position where the first magnetic pole is closest to the image carrier.