A developing unit includes a toner storage portion for containing toner and a development portion for containing the toner supplied from the toner storage portion. The development portion includes a developing roller for supplying the toner to a photosensitive body, a supply roller and an auxiliary supply roller. The supply roller and the auxiliary supply roller rotate while facing each other to supply the toner to the developing roller. In the developing unit, an inequality that |D−(R1+R2)|≦1.0 mm is satisfied, where a distance between the centers of the auxiliary supply roller and the supply roller in a region where the auxiliary supply roller and the supply roller face each other is D, a radius of the supply roller is R1, and a radius of the auxiliary supply roller is R2.