A developing unit for developing an electrostatic latent image formed on the outer peripheral surface of a latent image bearer rotating in one direction utilizes an electrified developer that is prepared by mixing two components, or an electrostatically chargeable toner and magnetic carrier. The developing unit includes a developing roller for supplying the developer to the latent image bearer and a carrier collecting roller disposed on the downstream side of the developing roller with respect to the rotational direction of the latent image bearer. The carrier collecting roller includes first and second magnetic pole elements of different magnetic polarities, both presenting a magnetic field intensity of 400 G to 750 G. The first magnetic pole element is disposed at a position on the opposite side across the center of the carrier collecting roller from the position opposing the latent image bearer. The second magnetic pole element is disposed at a position opposing the developing roller.