Magnetic brush-toner supply hopper

A developing machine for magnetic toner having a toner supply tank with an opening, a rotatable non-magnetic cylindrical shell disposed in said opening, its cylindrical surface partially protruding into the toner supply tank and a rotatable magnet roll disposed in said cylindrical shell, said magnet roll being adapted to rotate for drawing magnetic toner out of said toner supply tank, transporting the magnetic toner around said cylindrical shell to contact a support for electrostatic latent images and then drawing unused toner again into the toner supply tank, characterized in that the width of a first gap between a wall of the toner supply tank and the cylindrical shell for drawing unused magnetic toner back into the tank is made smaller than the maximum transportation depth for magnetic toner on the cylindrical shell and greater than both the width of a second gap between a wall of the toner supply tank and the cylindrical shell for drawing magnetic toner out of the supply tank and also the width of a third gap between the latent image support and the cylindrical shell, leakage through said first gap between the wall of the toner supply tank and the shell being prevented when the magnet roll and cylindrical shell are stationary, the plane defined by said first gap being oriented vertically at the bottom of the shell and wherein said unused toner drawn back into the toner supply tank through said first gap enters said first gap in a horizontal direction.