When image forming is performed by the photosensitive drum according to operating conditions corresponding to an image forming mode selected out of a predetermined plurality of candidates, the actualcumulative number of printed sheets Pi is corrected and recorded based on the image forming mode (monochrome mode or color mode; low-temperature and low humidity ambience mode or other ambience mode)selected at the time of each image forming (S7) and an adjustment volume (koxPia) of the charging applied voltage Ey is calculated and the charging applied voltage Ey is set based on the corrected cumulative number of printed sheets Pia (S5). As a result, the applied voltage Ey to a charging unit is changed according to the cumulative number of printed sheets and at the same time, a pace of changethereof is adjusted based on the image forming mode.