PURPOSE: To keep the quantity and the density of a toner, which is supplied from a hopper chamber to a developing chamber, constant independently of the quantity of the toner in the hopper chamber, by providing an aperture connected to external air in the hopper chamber, and keeping always the pressure of the inside of said hopper chamber in the atmospheric pressure.

CONSTITUTION: The upper part of a hopper chamber 14 and the upper part of a developing chamber 2 are connected through a tube 20 on the side face of a developing vessel 6. Thus, the pressure in the hopper chamber 14 is made euqal to the pressure in the developing chamber 2, namely the atmospheric pressure. Since this tube 20 is bent to be arranged apart from a side wall 21 of the developing vessel, this tube 20 functions as a handle when a developing device 1 is pulled out from, or is inserted, to a copying machine main body. Because of this connection between the hopper chamber 14 and the developing chamber 2, a toner floated by the oscillation of a toner receiving plate 13 is not leaked out from the developing device 1 even if it is scattered.