PURPOSE: To prevent the production of defective copies by detecting the remaining amount of the developer in an apparatus such as facsimile or the like and letting the first signal which warns the shortage of the developer and the second signal which warns the prohibition of use when the developer becomes further shorter.

CONSTITUTION: When the developing powder 6 in a hopper is gradually consumed, the amounts of the developing powder existing in small chambers 7, 8 also decrease and the quantity of light reaching a photo detector 10 from a light emitting lement 9 increases, causing the first signal to be emitted. At this stage, still several tens sheets of copying is feasible. As the remained developing powder is further consumed, the developing density begins to gradually decrease, causing the second signal to be outputted. By making double warnigns of developer shortage in this way, the production of defective copies may be prevented, downtime minimized and the sure and rapid reproduction and transmission of information in information processing machines accomplished.