PURPOSE: To prevent malfunction due to uneven distribution of toner, by providing a detecting member for the remaining amount of a developer which is made of a conductor to a side wall of a developer supplying means which contains the developer together with a developer carrier applied with an alternating bias voltage.

CONSTITUTION: A conductor 9 arranged extending in the axial direction of a sleeve 1 along the side wall in a hopper 6 is coated with an insulating material 10. This conductor 9 has shielding effect which prevents the evial influence of the alternating bias voltage applied to the sleeve 1 from leaking out of the hopper 6. The conductor 9 induces a potential difference corresponding to the AC potential applied to the sleeve 1. This potential difference varies with the amount of toner T between the sleeve 1 and conductor 9. For this purpose, this output potential difference is led from a contact 11 to a detecting circuit for the remaining amount of toner, thereby detecting how much the toner is left.