A developing device (50) includes a developing sleeve (53) for supplying toner particles (T) to a latent image area (22) on a peripheral surface of a photoconductive drum (20) while rotating about a central shaft (534). The developing sleeve (53) has an immovable sleeve magnet (533) therein. Two magnetic members (82) are disposed in opposite end portions of the developing sleeve (53) and are spaced a predetermined distance from the peripheral surface of the developing sleeve. Each magnet member (82) has an arc shape. A magnetic member magnet (83) is mounted in the magnet member (82) and faces a sleeve magnet (533) so that opposite facing portions of the magnetic member magnet (83) and the sleeve magnet (533) have the same polarity. With this construction, toner particles are prevented from leaking from the end portions of the developing sleeve (53).