PURPOSE: To make developing possible without scattering and dropping of a carrier despite the use of a resin coated spherical carrier by providing another auxiliary magnet before and behind the main magnet as a developing magnet thereby forming a developing ear by a dense developer with the low ear.

CONSTITUTION: A sleeve 10 which faces a photosensitive drum 16 and rotates in the direction opposite from that of the photosensitive drum is provided therein with a main developing magnet 7 of the width narrower than that of conventional developing magnets in the part of the axial center 2 facing the photosensitive drum. Another auxiliary developing magnets 6, 8 are disposed in proximity to the lower and upper part of said magnet 7, whereby the magnetic lines of force forming developing ears are formed together with the magnet 7. If the spacing between, for example, the magnet 7 and 8 is set at 50° and the spacing between the magnets 7 and 6 at 35°. a brush L2 of low ears is formed with high density despite the use of spherical carriers, and the developer is satisfactorily maintained and conveyed.