PURPOSE: To secure the picture quality of a copy and to prevent a damage to a photosensitive body, a toner scatter, etc., by setting the number of copies which can be taken previously and comparing this number with the remaining number of copies to be taken, and thus determining copy stop condition.

CONSTITUTION: A developer density detection sensor S, a developer supply device 21 which includes a supply roller 15 and a toner motor, a toner deficiency alarm lamp 22, an input signal processing part 24, and a memory device 25 are connected to a microcomputer 20. An input copy quantity is set in a counter C and a decision on the output of a developer density sensor S after a copying process is made. The decision result indicates OK when at 'H' or a deficiency in the amount of a developer when at 'L'. Consequently, if the deficiency in the amount of the developer is detected during multi-copying operation, the number of copies which can be taken without any deterioration in copy picture quality after the deficiency in the amount of the developer is detected is compared with the remaining number of copies to be taken; when the former is larger than the latter, all remaining copies are taken and when not, the copying operation is stopped immediately and an alarm state is entered.