An image forming apparatus includes an image forming portion configured to form a toner image. The image forming portion includes: a photosensitive body; a charging device; an exposure device; a toner supply device; and a transfer device. A continuously printed amount, which has been attained by the image forming portion while the image forming portion has formed toner images continuously with a time interval between every two successive image-forming timings having a length shorter than or equal to a prescribed length, is determined. A charging voltage to be applied to the charging device is set based on a sum of a reference charging voltage and a correction value, the reference charging voltage being determined based on a target surface potential of the photosensitive body, the correction value being determined based on the continuously printed amount.