A developing apparatus having a developing sleeve provided with an elastic layer on its surface, and for developing an electrostatic image formed on an image bearing member with a mono-component magnetic toner having a mean degree of circularity of 0.965 or greater, a magnet provided in the developing sleeve, and a blade for regulating the amount of the developer carried on the developing sleeve satisfies the expressions |Br|/|B|.gtoreq.0.5 and Nsb/(Bs.times.R).ltoreq.0.5, where B (G) is magnetic flux density formed on the surface of the developing sleeve by the magnet at the contact position between the blade and the developing sleeve, Nsb (mm) is the contact width between the blade and the developing sleeve, Br (G) is a component of magnetic flux density B (G) in a direction perpendicular to the surface of the developing sleeve, Bs (rad) is a half value width of the perpendicular component of the magnetic flux density of the nearest one of the magnetic poles of the magnet to the contact position on the surface of the developing sleeve, and R (mm) is the radius of the developing sleeve.