To stably form a high-quality image free from an image defect such as irregular image density by holding the surface potential of a photoreceptor nearly constant without complicating the configuration of an image forming apparatus all through the duration of service of the photoreceptor.
The electrifying device includes: an electrifier 2 equipped with a grid electrode 3, a discharge electrode 4 and a charger case 5; a power source 6 applying voltage to the grid electrode 3; a temperature and humidity detection means 7; a CPU 8; and an environment decision means, an operating time accumulation means, a wear-amount-of-film calculation means and an applied voltage calculation means which are incorporated in the storage part of the CPU 8. The wear-amount-of-film calculation means calculates the total wear amount of film of a photoreceptive film from a result of accumulation by the operating time accumulation means, and the applied voltage calculation means calculates voltage to be applied to the grid electrode 3 from the result of decision by the environment decision means and the result of calculation by the wear-amount-of-film calculation means. The voltage control means of the CPU 8 controls the application of the voltage to the grid electrode 3 based on a result of the calculation.
TSUJIMOTO AKIKO
YOSHIOKA TORU
TOMITA SHOJI
Takeshi Sugiyama
Shoji Ishida