To provide an image forming apparatus, an image formation system, a cartridge, and a memory medium, in which the space saving and cost reduction of a charging voltage circuit and highly accurate control of charging AC voltage can be attained.

The image forming apparatus comprises: a means for selecting a part of charging voltage outputted from a charging voltage output part during no formation of an image, outputting the selected charging voltage as detecting voltage and comparing a detected current value with a previously set target current value to determine a charging voltage for the formation of an image; and a control part for changing the detecting voltage to be selected in accordance with the consumption of an image carrier and determining the charging voltage corresponding to a minimum current value larger than the target current value out of current values detected by outputting the detecting voltage as the charging voltage for the formation of an image.