A developing device (5) includes a developer bearer (50) to carry, by rotation, developer including toner and magnetic carrier to a development range facing a latent image bearer (1) to bear a latent image. The developer bearer (50) includes a magnetic field generator (55) having multiple magnetic poles (P1, P2, P3, P4, P5) and a cylindrical developing sleeve (51) to rotate and bear developer on an outer circumferential surface thereof with magnetic force of the magnetic field generator (55) disposed inside the developing sleeve (51). The developing sleeve (51) receives development voltage including an AC component having a frequency of 2.0 kHz or lower, and a duty ratio of a component having a polarity opposite a toner normal charge polarity of the AC component is within a range from 4% to 20%.