A developing device includes first and second magnet members respectively including first and second transfer magnetic poles that have different polarities, that generate a magnetic force for transferring a developer from a first developer-transporting member to a second developer-transporting member, and that are located at positions where the developer-transporting members come close to each other, wherein (B1×B2)/L2 is less than about 400 where L represents a distance (mm) between an outer peripheral surface portion of the first developer-transporting member, the portion facing the first transfer magnetic pole, and an outer peripheral surface portion of the second developer-transporting member, the portion facing the second transfer magnetic pole, and B1 and B2 (mT) respectively represent maximum magnetic flux densities of the first and second transfer magnetic poles in a normal line direction on outer peripheral surfaces of the first and second developer-transporting members.