PURPOSE: To effectively use a photosensitive body by preventing a waste toner holding part from being filled with waste toner, without increasing cost and size.

CONSTITUTION: A process unit A is provided with at least a photo-sensitive drum 1 and the waste toner holding part 42 integrally. In a developing device 3, a hopper 31 can be replenished with a fixed amount of toner T. The total amount of use of the photosensitive drum 1 (for example, the number of rotations) are counted by a counter 6, and the total amount of consumption of the toner T in the hopper 31 (for example, the number of times that toner replenishment is carried out) is counted by a counter 9. A comparison arithmetic part 10 compares the total amount of use of the photosensitive drum 1, counted by the counter 6, with the prescribed first reference value, and also compares the total amount of consumed toner T, counted by the counter 9, with the prescribed second reference value; and it decides the need to replace the process unit A, according to the total amount of use of the photosensitive drum 1 exceeds the first reference value or the total amount of consumed toner T exceeds the second reference value.