a charging apparatus and method used in an image forming apparatus uses a charging apparatus to apply a charging potential to a photosensitive body , a voltage measuring device that measures the charging potential and outputs a measured charging potential signal , an environmental condition sensor which senses at least one environmental condition and outputs an environmental condition signal , and adjustable voltage application which applies an applied voltage to said charging member , and a controller , where the controller controls an amount of the applied voltage applied to the charging member in accordance with the charging potential signal and the environmental signal , where the applied voltage is adjusted to compensate for the sensed environmental condition .