PURPOSE: To prevent malfunction due to the adhesion of a toner to a detecting means, by providing a toner receiving member and a means which detects whether the toner exists on this member or not, in the course through which the toner is supplied from a toner supply device to a developer chamber.

CONSTITUTION: A thick disc-shaped toner receiving member 11, a light projector and receiver 12 as a toner detecting means, and a toner scraping plate 13 are provided in the toner supply course in the upper part of a developer chamber 18 surrounded with a housing 17. When a supply toner 22 exists in a hopper 14, the toner 22 is supplied into the developer chamber 18 in accordance with the rotation of a toner supply roller 16 by every prescribed quantity. In this case, a part of the dropped toner 22 falls onto the upper face of the toner receiving member 11 and is stuck onto the outside circumferential face of the member 11 and is turned, and it is detected by the light projector and receiver 12 that the toner is supplied.