Provided is an image forming apparatus capable of appropriately setting a range of a charging voltage for electrically charging an image bearing member. A charging roller (2) and a charging power source (S1) are configured to apply a voltage between the charging roller (2) and a photosensitive drum (1) to electrically charge the photosensitive drum (1). A control circuit (13) is configured to set a voltage for obtaining a predetermined discharge current by the charging roller (2) with the photosensitive drum (1). The control circuit (13) is configured to determine, depending on a state of a resistance acting on an electric current flowing between the charging roller (2) and the photosensitive drum (1), at least one of an upper limit or a lower limit of the voltage set by the control circuit (13).