Patent ID: 8660470

Claim:
A developing device comprising: a first developer carrier and a second developer carrier that are disposed so as to face an image carrier, the first and second developer carriers facing each other in a facing region with a small distance therebetween, the first and second developer carriers respectively including a first magnetic member and a second magnetic member that are respectively magnetized with a first facing magnetic pole and a second facing magnetic pole that are located in parts of the first and second magnetic members in the facing region, the first and second facing magnetic poles having opposite polarities, and a first cylindrical member and a second cylindrical member that are respectively disposed around outer peripheries of the first and second magnetic members, the first and second cylindrical members rotating in opposite directions from the facing region toward the image carrier; a regulating member that regulates a layer thickness of developer that is supplied to at least one of the first and second developer carriers; and a separation member that separates the developer, whose layer thickness has been regulated by the regulating member, so that the developer is supplied toward the first developer carrier and toward the second developer carrier, the separation member being disposed such that distances between the separation member and the first and second developer carriers are the smallest in a region in which a magnitude of a combined magnetic field of the first and second facing magnetic poles of the first and second developer carriers locally decreases as compared with a case where at least one of the first and second developer carriers is independently disposed due to interaction between the first and second facing magnetic poles, the region being determined by analyzing the combined magnetic field.