An image forming apparatus includes an image bearing member; a first charging member for electrically charging the image bearing member by being supplied with an oscillating voltage in the form of a DC voltage biased with a common AC voltage during image formation; a second charging member, provided downstream of the first charging member with respect to a movement direction of the image bearing member, for electrically charging the image bearing member by being supplied with the DC voltage and the common AC voltage during the image formation; detecting portion for detecting an AC current passing through the second charging member; and a setting portion for setting, on the basis of a detection result of the detecting portion when a predetermined AC voltage is applied to the second charging member during non-image formation, the common AC voltage applied to the first charging member and the second charging member during the image formation so that a discharge current between the second charging member and the image bearing member is a predetermined value.