A developing unit is configured to develop an electrostatic latent image born on an image bearing member with a developer that has been charged by mixing and agitating toner and magnetic carrier. The developing unit comprises a developing hopper; a developer bearing member; and at least a pair of agitating and conveying members rotationally driven in the developing hopper. The agitating and conveying members are arranged substantially parallel to the developer bearing member and each rotational shaft of the agitating and conveying members is embedded with a magnetic source element whose magnetic poles are laid out so as to produce a magnetic field radially oriented in a particular fixed direction with respect to the agitating and conveying member.