A magnetic brush developing device comprising a developing roller including a cylindrical stationary magnet and a sleeve rotatably mounted around the magnet, the developing roller being disposed adjacent the surface of a latent image bearing member, the cylindrical magnet having a developing magnetic pole facing the surface of the latent image forming member and transporting magnetic poles respectively disposed above and below the developing magnetic pole in adjacent relation thereto, the transporting magnetic poles being narrower in width than and having an opposite polarity to the developing magnetic pole.